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Abstract:

A method of manufacturing an arthroplasty jig is disclosed herein. The
method may include the following: generate two dimensional image data of
a patient joint to undergo arthroplasty, identify in the two dimensional
image data a first point corresponding to an articular surface of a bone
forming the joint, identify a second point corresponding to an articular
surface of an implant, identify a location of a resection plane when the
first point is correlated with the second point, and create the
arthroplasty jig with a resection guide located according to the
identified location of the resection plane.

Claims:

1. A method of manufacturing an arthroplasty jig, the method
comprising:generate two dimensional image data of a patient joint to
undergo arthroplasty;identify in the two dimensional image data a first
point corresponding to an articular surface of a bone forming the
joint;identify a second point corresponding to an articular surface of an
implant;identify a location of a resection plane when the first point is
correlated with the second point; andcreate the arthroplasty jig with a
resection guide located according to the identified location of the
resection plane.

2. The method of claim 1, wherein the articular surface of the bone
forming the joint is a femoral condylar surface, and the articular
surface of the implant is a condylar surface of a femoral implant.

3. The method of claim 2, wherein the first point includes a most distal
point on the femoral condylar surface.

4. The method of claim 3, wherein the most distal point on the femoral
condylar surface includes a most distal point on a healthy femoral
condyle and another point on or near an unhealthy femoral condyle, the
another point being on a joint line extending from the most distal point
on the healthy femoral condyle.

5. The method of claim 4, wherein the joint line is perpendicular to a
line defined along a trochlear groove.

6. The method of claim 3, wherein the first point further includes a most
proximal point on the femoral condylar surface.

7. The method of claim 6, wherein the most proximal point on the femoral
condylar surface includes a most proximal point on a healthy femoral
condyle and another point on or near an unhealthy femoral condyle, the
another point being on a joint line extending from the most proximal
point on the healthy femoral condyle.

8. The method of claim 7, wherein the joint line is perpendicular to a
line defined along a trochlear groove.

9. The method of claim 1, wherein the first and second points are
correlated in a two dimensional comparison.

10. The method of claim 1, wherein the first point is identified in a
coronal view or an axial view of the two dimensional image data.

11. The method of claim 10, wherein the first point is correlated with the
second point in a sagittal view.

12. The method of claim 1, wherein the articular surface of the bone
forming the joint is a tibia condylar surface, and the articular surface
of the implant is a condylar surface of a tibia implant.

13. The method of claim 12, wherein the first point includes a most
posterior point on the tibia condylar surface and a most anterior point
on the tibia condylar surface.

14. The method of claim 13, wherein the most posterior and most anterior
points on the tibia condylar surface include a most posterior point and a
most anterior point on a healthy tibia condyle and a most posterior point
and a most anterior point on or near an unhealthy tibia condyle, wherein
the most posterior and most anterior points on the healthy tibia condyle
are on a first line, and the most posterior and most anterior points on
or near the unhealthy tibia condyle are on a second line parallel to the
first line.

15. The method of claim 14, wherein the first point further includes a
most distal point on the healthy tibia condyle and a most distal point on
or near the unhealthy tibia condyle.

16. The method of claim 15, wherein the most distal point on the healthy
tibia condyle is on the first line and the most distal point on or near
the unhealthy tibia condyle is on the second line.

17. The method of claim 1, wherein the first point is identified in a
coronal view or a sagittal view of the two dimensional image data.

18. The method of claim 17, wherein the first point is correlated with the
second point in an axial view.

19. The method of claim 1, wherein creating the arthroplasty jig with a
resection guide located according to the identified location of the
resection plane includes providing a jig blank and using CNC to transform
the jig blank into the arthroplasty jig.

20. The method of claim 1, wherein creating the arthroplasty jig with a
resection guide located according to the identified location of the
resection plane includes employing rapid prototyping to generate the
arthroplasty jig.

21. The method of claim 20, wherein the rapid prototyping includes SLA.

22. The method of claim 1, further comprising evaluating the implant for
size when the first point is correlated with the second point.

23. The method of claim 22, wherein evaluating the implant for size
includes selecting the implant from a plurality of candidate implants.

24. The method of claim 1, wherein the two dimensional image data is
obtained from a MRI or CT of the patient joint.

25. An arthroplasty jig manufactured according to the method of claim 1.

26. A method of manufacturing an arthroplasty jig, the method
comprising:a) identify a first attribute in a coronal image and a second
attribute in an axial image, wherein the attributes are associated with a
bone forming a portion of a patient joint;b) place the first and second
attributes in a sagittal relationship;c) compare in the sagittal
relationship the first and second attributes to respective corresponding
attributes of a plurality of candidate prosthetic implants;d) select a
prosthetic implant from the comparison of step c;e) correlate in the
sagittal relationship the first and second attributes to respective
corresponding attributes of the prosthetic implant;f) identify the
location of a resection plane associated with the prosthetic implant
during the correlation of step e; andg) create the arthroplasty jig with
a resection guide located according to the identified location of the
resection plane.

27. The method of claim 26, wherein at least one of the images is obtained
from a MRI or CT of the patient joint.

28. The method of claim 26, wherein the bone is a femur.

29. The method of claim 28, wherein the first attribute and second
attribute are associated with an articular surface of the femur.

30. The method of claim 29, wherein the first attribute includes a most
distal point on a condyle of the femur.

31. The method of claim 29, wherein the second attribute includes a most
posterior point on a condyle of the femur.

32. The method of claim 29, wherein the first attribute includes a most
distal point on a condyle of the femur and the second attribute includes
a most posterior point on the condyle of the femur.

33. The method of claim 32, wherein the respective corresponding
attributes of the prosthetic implant of step e include a most distal
point on a condyle of the prosthetic implant and a most posterior point
on the condyle of the prosthetic implant.

34. The method of claim 26, wherein the arthroplasty jig is created via
CNC or SLA.

35. A method of manufacturing an arthroplasty jig, the method
comprising:a) identify first and second attributes in a sagittal image,
wherein the attributes are associated with a bone forming a portion of a
patient joint;b) place the first and second attributes in an axial
relationship;c) compare in the axial relationship the first and second
attributes to respective corresponding attributes of a plurality of
candidate prosthetic implants;d) select a prosthetic implant from the
comparison of step c;e) correlate in the axial relationship the first and
second attributes to respective corresponding attributes of the
prosthetic implant;f) identify the location of a resection plane
associated with the prosthetic implant during the correlation of step e;
andg) create the arthroplasty jig with a resection guide located
according to the identified location of the resection plane.

36. The method of claim 35, wherein at least one of the images is obtained
from a MRI or CT of the patient joint.

37. The method of claim 35, wherein the bone is a tibia.

38. The method of claim 37, wherein the first attribute and second
attribute are associated with an articular surface of the tibia.

39. The method of claim 38, wherein the first attribute includes a most
anterior point on a condyle of the tibia.

40. The method of claim 38, wherein the second attribute includes a most
posterior point on a condyle of the tibia.

41. The method of claim 38, wherein the first attribute includes a most
anterior point on a condyle of the tibia and the second attribute
includes a most posterior point on the condyle of the tibia.

42. The method of claim 41, wherein the respective corresponding
attributes of the prosthetic implant of step e include a most anterior
point on a condyle of the prosthetic implant and a most posterior point
on the condyle of the prosthetic implant.

43. The method of claim 35, wherein the arthroplasty jig is created via
CNC or SLA.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS

[0001]The present application claims priority to U.S. Patent Application
No. 61/102,692, which was filed Oct. 3, 2008, and entitled Arthroplasty
System and Related Methods. The present application is also a
continuation-in-part of U.S. patent application Ser. No. 11/959,344,
which was filed Dec. 18, 2007, and entitled System and Method for
Manufacturing Arthroplasty Jigs. The present application claims priority
to all of the above-mentioned applications and hereby incorporates by
reference all of the above-mentioned applications in their entireties
into the present application.

FIELD OF THE INVENTION

[0002]The present invention relates to customized arthroplasty cutting
jigs. More specifically, the present invention relates to systems and
methods of manufacturing such jigs.

BACKGROUND OF THE INVENTION

[0003]Over time and through repeated use, bones and joints can become
damaged or worn. For example, repetitive strain on bones and joints
(e.g., through athletic activity), traumatic events, and certain diseases
(e.g., arthritis) can cause cartilage in joint areas, which normally
provides a cushioning effect, to wear down. When the cartilage wears
down, fluid can accumulate in the joint areas, resulting in pain,
stiffness, and decreased mobility.

[0004]Arthroplasty procedures can be used to repair damaged joints. During
a typical arthroplasty procedure, an arthritic or otherwise dysfunctional
joint can be remodeled or realigned, or an implant can be implanted into
the damaged region. Arthroplasty procedures may take place in any of a
number of different regions of the body, such as a knee, a hip, a
shoulder, or an elbow.

[0005]One type of arthroplasty procedure is a total knee arthroplasty
("TKA"), in which a damaged knee joint is replaced with prosthetic
implants. The knee joint may have been damaged by, for example, arthritis
(e.g., severe osteoarthritis or degenerative arthritis), trauma, or a
rare destructive joint disease. During a TKA procedure, a damaged portion
in the distal region of the femur may be removed and replaced with a
metal shell, and a damaged portion in the proximal region of the tibia
may be removed and replaced with a channeled piece of plastic having a
metal stem. In some TKA procedures, a plastic button may also be added
under the surface of the patella, depending on the condition of the
patella.

[0006]Implants that are implanted into a damaged region may provide
support and structure to the damaged region, and may help to restore the
damaged region, thereby enhancing its functionality. Prior to
implantation of an implant in a damaged region, the damaged region may be
prepared to receive the implant. For example, in a knee arthroplasty
procedure, one or more of the bones in the knee area, such as the femur
and/or the tibia, may be treated (e.g., cut, drilled, reamed, and/or
resurfaced) to provide one or more surfaces that can align with the
implant and thereby accommodate the implant.

[0007]Accuracy in implant alignment is an important factor to the success
of a TKA procedure. A one- to two-millimeter translational misalignment,
or a one- to two-degree rotational misalignment, may result in imbalanced
ligaments, and may thereby significantly affect the outcome of the TKA
procedure. For example, implant misalignment may result in intolerable
post-surgery pain, and also may prevent the patient from having full leg
extension and stable leg flexion.

[0008]To achieve accurate implant alignment, prior to treating (e.g.,
cutting, drilling, reaming, and/or resurfacing) any regions of a bone, it
is important to correctly determine the location at which the treatment
will take place and how the treatment will be oriented. In some methods,
an arthroplasty jig may be used to accurately position and orient a
finishing instrument, such as a cutting, drilling, reaming, or
resurfacing instrument on the regions of the bone. The arthroplasty jig
may, for example, include one or more apertures and/or slots that are
configured to accept such an instrument.

[0009]A system and method has been developed for producing customized
arthroplasty jigs configured to allow a surgeon to accurately and quickly
perform an arthroplasty procedure that restores the pre-deterioration
alignment of the joint, thereby improving the success rate of such
procedures. Specifically, the customized arthroplasty jigs are indexed
such that they matingly receive the regions of the bone to be subjected
to a treatment (e.g., cutting, drilling, reaming, and/or resurfacing).
The customized arthroplasty jigs are also indexed to provide the proper
location and orientation of the treatment relative to the regions of the
bone. The indexing aspect of the customized arthroplasty jigs allows the
treatment of the bone regions to be done quickly and with a high degree
of accuracy that will allow the implants to restore the patient's joint
to a generally pre-deteriorated state. However, the system and method for
generating the customized jigs may rely on a plurality of images from a
MRI scan or CT scan to construct a 3D bone model. The image slice
orientation of the MRI scan or CT scan is at least partially dependent
upon the imaging system operator to place the localizer in various
positions during the scan. This imaging process is subject to operator
error, such as inaccurate placement of the localizer, thereby increasing
the time, manpower and costs associated with producing the customized
arthroplasty jig.

[0010]There is a need in the art for a system and method for reducing the
labor associated with generating customized arthroplasty jigs. There is
also a need in the art for a system and method for reducing the effects
of operator error and thereby increasing the accuracy of customized
arthroplasty jigs.

SUMMARY

[0011]Various embodiments of a method of manufacturing an arthroplasty jig
are disclosed herein. In a first embodiment, the method may include the
following: generate two dimensional image data of a patient joint to
undergo arthroplasty, identify in the two dimensional image data a first
point corresponding to an articular surface of a bone forming the joint,
identify a second point corresponding to an articular surface of an
implant, identify a location of a resection plane when the first point is
correlated with the second point, and create the arthroplasty jig with a
resection guide located according to the identified location of the
resection plane.

[0012]In a second embodiment, the method may include the following: (a)
identify a first attribute in a coronal image and a second attribute in
an axial image, wherein the attributes are associated with a bone forming
a portion of a patient joint, (b) place the first and second attributes
in a sagittal relationship, (c) compare in the sagittal relationship the
first and second attributes to respective corresponding attributes of a
plurality of candidate prosthetic implants, (d) select a prosthetic
implant from the comparison of step c, (e) correlate in the sagittal
relationship the first and second attributes to respective corresponding
attributes of the prosthetic implant, (f) identify the location of a
resection plane associated with the prosthetic implant during the
correlation of step e, and (g) create the arthroplasty jig with a
resection guide located according to the identified location of the
resection plane.

[0013]In a third embodiment, the method may include the following: (a)
identify first and second attributes in a sagittal image, wherein the
attributes are associated with a bone forming a portion of a patient
joint, (b) place the first and second attributes in an axial
relationship, (c) compare in the axial relationship the first and second
attributes to respective corresponding attributes of a plurality of
candidate prosthetic implants, (d) select a prosthetic implant from the
comparison of step c, (e) correlate in the axial relationship the first
and second attributes to respective corresponding attributes of the
prosthetic implant, (f) identify the location of a resection plane
associated with the prosthetic implant during the correlation of step e,
and (g) create the arthroplasty jig with a resection guide located
according to the identified location of the resection plane.

[0014]While multiple embodiments are disclosed, still other embodiments of
the present invention will become apparent to those skilled in the art
from the following detailed description, which shows and describes
illustrative embodiments of the invention. As will be realized, the
invention is capable of modifications in various aspects, all without
departing from the spirit and scope of the present invention.
Accordingly, the drawings and detailed description are to be regarded as
illustrative in nature and not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1A is a schematic diagram of a system for employing the
automated jig production method disclosed herein.

[0019]FIG. 3A is an isometric view of a 3D computer model of a femur lower
end and a 3D computer model of a tibia upper end in position relative to
each to form a knee joint and representative of the femur and tibia in a
non-degenerated state.

[0020]FIG. 3B is an isometric view of a 3D computer model of a femur
implant and a 3D computer model of a tibia implant in position relative
to each to form an artificial knee joint.

[0021]FIG. 4 is a perspective view of the distal end of 3D model of the
femur wherein the femur reference data is shown.

[0022]FIG. 5A is a sagittal view of a femur illustrating the orders and
orientations of imaging slices utilized in the femur POP.

[0023]FIG. 5B depicts axial imaging slices taken along section lines of
the femur of FIG. 5A.

[0024]FIG. 5C depicts coronal imaging slices taken along section lines of
the femur of FIG. 5A.

[0025]FIG. 6A is an axial imaging slice taken along section lines of the
femur of FIG. 5A, wherein the distal reference points are shown.

[0026]FIG. 6B is an axial imaging slice taken along section lines of the
femur of FIG. 5A, wherein the trochlear groove bisector line is shown.

[0027]FIG. 6C is an axial imaging slice taken along section lines of the
femur of FIG. 5A, wherein the femur reference data is shown.

[0028]FIG. 6D is the axial imaging slices taken along section lines of the
femur in FIG. 5A.

[0029]FIG. 7A is a coronal slice taken along section lines of the femur of
FIG. 5A, wherein the femur reference data is shown

[0030]FIG. 7B is the coronal imaging slices taken along section lines of
the femur in FIG. 5A.

[0096]Disclosed herein are customized arthroplasty jigs 2 and systems 4
for, and methods of, producing such jigs 2. The jigs 2 are customized to
fit specific bone surfaces of specific patients. Depending on the
embodiment, the jigs 2 are automatically planned and generated and may be
similar to those disclosed in these three U.S. patent applications: U.S.
patent application Ser. No. 11/656,323 to Park et al., titled
"Arthroplasty Devices and Related Methods" and filed Jan. 19, 2007; U.S.
patent application Ser. No. 10/146,862 to Park et al., titled "Improved
Total Joint Arthroplasty System" and filed May 15, 2002; and U.S. patent
Ser. No. 11/642,385 to Park et al., titled "Arthroplasty Devices and
Related Methods" and filed Dec. 19, 2006. The disclosures of these three
U.S. patent applications are incorporated by reference in their
entireties into this Detailed Description.

[0097]A. Overview of System and Method for Manufacturing Customized
Arthroplasty Cutting Jigs

[0098]For an overview discussion of the systems 4 for, and methods of,
producing the customized arthroplasty jigs 2, reference is made to FIGS.
1A-1E. FIG. 1A is a schematic diagram of a system 4 for employing the
automated jig production method disclosed herein. FIGS. 1B-1E are flow
chart diagrams outlining the jig production method disclosed herein. The
following overview discussion can be broken down into three sections.

[0099]The first section, which is discussed with respect to FIG. 1A and
[blocks 100-125] of FIGS. 1B, 1C1, 1C2, and 1E, pertains to an example
method of determining, in a two-dimensional ("2D") computer model
environment, saw cut and drill hole locations 30, 32 relative to 2D
images 16 of a patient's joint 14. The resulting "saw cut and drill hole
data" 44 is planned to provide saw cuts 30 and drill holes 32 that will
allow arthroplasty implants to restore the patient's joint to its
pre-degenerated or natural alignment state.

[0100]The second section, which is discussed with respect to FIG. 1A and
[blocks 100-105 and 130-145] of FIGS. 1B, 1D, and 1E, pertains to an
example method of importing into 3D computer generated jig models 38 3D
computer generated surface models 40 of arthroplasty target areas 42 of
3D computer generated arthritic models 36 of the patient's joint bones.
The resulting "jig data" 46 is used to produce a jig customized to
matingly receive the arthroplasty target areas of the respective bones of
the patient's joint.

[0101]The third section, which is discussed with respect to FIG. 1A and
[blocks 150-165] of FIG. 1E, pertains to a method of combining or
integrating the "saw cut and drill hole data" 44 with the "jig data" 46
to result in "integrated jig data" 48. The "integrated jig data" 48 is
provided to the CNC machine 10 or other rapid production machine (e.g., a
stereolithography apparatus ("SLA") machine) for the production of
customized arthroplasty jigs 2 from jig blanks 50 provided to the CNC
machine 10. The resulting customized arthroplasty jigs 2 include saw cut
slots and drill holes positioned in the jigs 2 such that when the jigs 2
matingly receive the arthroplasty target areas of the patient's bones,
the cut slots and drill holes facilitate preparing the arthroplasty
target areas in a manner that allows the arthroplasty joint implants to
generally restore the patient's joint line to its pre-degenerated state
or natural alignment state.

[0102]As shown in FIG. 1A, the system 4 includes a computer 6 having a CPU
7, a monitor or screen 9 and an operator interface controls 11. The
computer 6 is linked to a medical imaging system 8, such as a CT or MRI
machine 8, and a computer controlled machining system 10, such as a CNC
milling machine 10.

[0103]As indicated in FIG. 1A, a patient 12 has a joint 14 (e.g., a knee,
elbow, ankle, wrist, hip, shoulder, skull/vertebrae or
vertebrae/vertebrae interface, etc.) to be replaced. The patient 12 has
the joint 14 scanned in the imaging machine 8. The imaging machine 8
makes a plurality of scans of the joint 14, wherein each scan pertains to
a thin slice of the joint 14.

[0104]As can be understood from FIG. 1B, the plurality of scans is used to
generate a plurality of two-dimensional ("2D") images 16 of the joint 14
[block 100]. Where, for example, the joint 14 is a knee 14, the 2D images
will be of the femur 18 and tibia 20. The imaging may be performed via CT
or MRI. In one embodiment employing MRI, the imaging process may be as
disclosed in U.S. patent application Ser. No. 11/946,002 to Park, which
is entitled "Generating MRI Images Usable For The Creation Of 3D Bone
Models Employed To Make Customized Arthroplasty Jigs," was filed Nov. 27,
2007 and is incorporated by reference in its entirety into this Detailed
Description. The images 16 may be a variety of orientations, including,
for example, sagittal 2D images, coronal 2D images and axial 2D images.

[0105]As can be understood from FIG. 1A, the 2D images are sent to the
computer 6 for analysis and for creating computer generated 2D models and
3D models. In one embodiment, the bone surface contour lines of the bones
18, 20 depicted in the image slices 16 may be auto segmented via a image
segmentation process as disclosed in U.S. Patent Application 61/126,102,
which was filed Apr. 30, 2008, is entitled System and Method for Image
Segmentation in Generating Computer Models of a Joint to Undergo
Arthroplasty, and is hereby incorporated by reference into the present
application in its entirety.

[0106]As indicated in FIG. 1B, in one embodiment, reference point W is
identified in the 2D images 16 [block 105]. In one embodiment, as
indicated in [block 105] of FIG. 1A, reference point W may be at the
approximate medial-lateral and anterior-posterior center of the patient's
joint 14. In other embodiments, reference point W may be at any other
location in the 2D images 16, including anywhere on, near or away from
the bones 18, 20 or the joint 14 formed by the bones 18, 20. Reference
point W may be defined at coordinates (X0-j, Y0-j, Z0-j)
relative to an origin (X0, Y0, Z0) of an X-Y-Z axis and
depicted in FIGS. 1B-1D as W (X0-j, Y0-j, Z0-j).
Throughout the processes described herein, to allow for correlation
between the different types of images, models or any other data created
from the images, movements of such images, models or any other data
created form the images may be tracked and correlated relative to the
origin.

[0107]As described later in this overview, point W may be used to locate
the 2D images 16 and computer generated 3D model 36 created from the 2D
images 16 respectively with the implant images 34 and jig blank model 38
and to integrate information generated via the POP process. Depending on
the embodiment, point W, which serves as a position and/or orientation
reference, may be a single point, two points, three points, a point plus
a plane, a vector, etc., so long as the reference point W can be used to
position and/or orient the 2D images 16, 34 and 3D models 36, 38 relative
to each other as needed during the POP process.

[0108]As shown in FIG. 1C1, the coronal and axial 2D images 16 of the
femur 18 forming the patient's joint 14 are analyzed to determine femur
reference data [block 110]. For example, the coronal 2D images are
analyzed to determine the most distal femur point D1 on a healthy
condyle and a joint line perpendicular to a trochlear groove line is used
to estimate the location of a hypothetical most distal point D2 on
the damaged condyle. Similarly, the axial 2D images are analyzed to
determine the most posterior femur point P1 on a healthy condyle and
a joint line perpendicular to a trochlear groove line is used to estimate
the location of a hypothetical most posterior point P2 on the
damaged condyle. The femur reference data points D1, D2,
P1, P2 is mapped or otherwise imported to a sagittal or y-z
plane in a computer environment and used to determine the sagittal or y-z
plane relationship between the femur reference data points D1,
D2, P1, P2. The femur reference data D1, D2,
P1, P2 is then used to choose candidate femoral implant(s).
[Block 112]. The femur reference data points D1, D2, P1,
P2 are respectively correlated with similar reference data points
D1', D2', P1', P2 of the selected femur implant 34 in
a sagittal or y-z plane [block 114]. This correlation determines the
locations and orientations of the cut plane 30 and drill holes 32 needed
to cause the patient's joint to returned to a natural, pre-deteriorated
alignment with the selected implant 34. The cut plane 30 and drill hole
32 locations determined in block 114 are adjusted to account for
cartilage thickness [block 118].

[0109]As shown in FIG. 1C2 at block 120, tibia reference data is
determined from the images in a manner similar to the process of block
110, except different image planes are employed. Specifically, sagittal
and coronal images slices of the tibia are analyzed to identify the
lowest (i.e., most distal) and most anterior and posterior points of the
tibia recessed condylar surfaces. This tibia reference data is then
projected onto an axial view. The tibia reference data is used to select
an appropriate tibia implant [Block 121]. The tibia reference data is
correlated to similar reference data of the selected tibia implant in a
manner similar to that of block 114, except the correlation takes place
in an axial view [Block 122]. The cut plane 30 associated with the tibia
implant's position determined according to block 122 is adjusted to
account for cartilage thickness [Block 123].

[0110]Once the saw cut locations 30 and drill hole locations 32 associated
with the POP of the femur and tibia implants 34 has been completed with
respect to the femur and tibia data 28 (e.g., the 2D femur and tibia
images 16 and reference point W), the saw cut locations 30 and drill hole
locations 32 are packaged relative to the reference point W(X0-j,
Y0-j, Z0-j) [Block 124]. As the images 16 and other data
created from the images or by employing the images may have moved during
any of the processes discussed in blocks 110-123, the reference point
W(X0-j, Y0-j, Z0-j) for the images or associated data may
become updated reference point W' at coordinates (X0-k, Y0-k,
Z0-k) relative to an origin (X0, Y0, Z0) of an X-Y-Z
axis. For example, during the correlation process discussed in blocks 114
and 122, the implant reference data may be moved towards the bone image
reference data or, alternatively, the bone image reference data may be
moved towards the implant reference data. In the later case, the location
of the bone reference data will move from reference point W(X0-j,
Y0-j, Z0-j) to updated reference point W'(X0-k, Y0-k,
Z0-k), and this change in location with respect to the origin will
need to be matched by the arthritic models 36 to allow for "saw cut and
drill hole" data 44 obtained via the POP process of blocks 110-125 to be
merged with "jig data" 46 obtained via the jig mating surface defining
process of blocks 130-145, as discussed below.

[0111]As can be understood from FIG. 1E, the POP process may be completed
with the packaging of the saw cut locations 30 and drill hole locations
32 with respect to the updated reference point W'(X0-k, Y0-k,
Z0-k) as "saw cut and drill hole data" 44 [Block 125]. The "saw cut
and drill hole data" 44 is then used as discussed below with respect to
[block 150] in FIG. 1E.

[0112]In one embodiment, the POP procedure is a manual process, wherein 2D
bone images 28 (e.g., femur and tibia 2D images in the context of the
joint being a knee) are manually analyzed to determine reference data to
aid in the selection of a respective implant 34 and to determine the
proper placement and orientation of saw cuts and drill holes that will
allow the selected implant to restore the patient's joint to its natural,
pre-deteriorated state. (The reference data for the 2D bone images 28 may
be manually calculated or calculated by a computer by a person sitting in
front of a computer 6 and visually observing the images 28 on the
computer screen 9 and determining the reference data via the computer
controls 11. The data may then be stored and utilized to determine the
candidate implants and proper location and orientation of the saw cuts
and drill holes. In other embodiments, the POP procedure is totally
computer automated or a combination of computer automation and manual
operation via a person sitting in front of the computer.

[0113]In some embodiments, once the selection and placement of the implant
has been achieved via the 2D POP processes described in blocks 110-125,
the implant selection and placement may be verified in 2D by
superimposing the implant models 34 over the bone images data, or vice
versa. Alternatively, once the selection and placement of the implant has
been achieved via the 2D POP processes described in blocks 110-125, the
implant selection and placement may be verified in 3D by superimposing
the implant models 34 over 3D bone models generated from the images 16.
Such bone models may be representative of how the respective bones may
have appeared prior to degeneration. In superimposing the implants and
bones, the joint surfaces of the implant models can be aligned or caused
to correspond with the joint surfaces of the 3D bone models. This ends
the overview of the POP process. A more detailed discussion of various
embodiments of the POP process is provided later in this Detailed
Description

[0114]As can be understood from FIG. 1D, the 2D images 16 employed in the
2D POP analysis of blocks 110-124 of FIGS. 1C1-1C2 are also used to
create computer generated 3D bone and cartilage models (i.e., "arthritic
models") 36 of the bones 18, 20 forming the patient's joint 14 [block
130]. Like the above-discussed 2D images and femur and tibia reference
data, the arthritic models 36 are located such that point W is at
coordinates (X0-j, Y0-j, Z0-j) relative to the origin
(X0, Y0, Z0) of the X-Y-Z axis [block 130]. Thus, the 2D
images and femur and tibia data of blocks 110-125 and arthritic models 36
share the same location and orientation relative to the origin (X0,
Y0, Z0). This position/orientation relationship is generally
maintained throughout the process discussed with respect to FIGS. 1B-1E.
Accordingly, movements relative to the origin (X0, Y0, Z0)
of the 2D images and femur and tibia data of blocks 110-125 and the
various descendants thereof (i.e., bone cut locations 30 and drill hole
locations 32) are also applied to the arthritic models 36 and the various
descendants thereof (i.e., the jig models 38). Maintaining the
position/orientation relationship between the 2D images and femur and
tibia data of blocks 110-125 and arthritic models 36 and their respective
descendants allows the "saw cut and drill hole data" 44 to be integrated
into the "jig data" 46 to form the "integrated jig data" 48 employed by
the CNC machine 10 to manufacture the customized arthroplasty jigs 2, as
discussed with respect to block 150 of FIG. 1E.

[0115]Computer programs for creating the 3D computer generated arthritic
models 36 from the 2D images 16 include: Analyze from AnalyzeDirect,
Inc., Overland Park, Kans.; Insight Toolkit, an open-source software
available from the National Library of Medicine Insight Segmentation and
Registration Toolkit ("ITK"), www.itk.org; 3D Slicer, an open-source
software available from www.slicer.org; Mimics from Materialise, Ann
Arbor, Mich.; and Paraview available at www.paraview.org.

[0116]The arthritic models 36 depict the bones 18, 20 in the present
deteriorated condition with their respective degenerated joint surfaces
24, 26, which may be a result of osteoarthritis, injury, a combination
thereof, etc. The arthritic models 36 also include cartilage in addition
to bone. Accordingly, the arthritic models 36 depict the arthroplasty
target areas 42 generally as they will exist when the customized
arthroplasty jigs 2 matingly receive the arthroplasty target areas 42
during the arthroplasty surgical procedure.

[0117]As indicated in FIG. 1D and already mentioned above, to coordinate
the positions/orientations of the 2D images and femur and tibia data of
blocks 110-125 and arthritic models 36 and their respective descendants,
any movement of the 2D images and femur and tibia data of blocks 110-125
from point W to point W' is tracked to cause a generally identical
displacement for the "arthritic models" 36, and vice versa [block 135].

[0119]In one embodiment, the procedure for indexing the jig models 38 to
the arthroplasty target areas 42 is a manual process. The 3D computer
generated models 36, 38 are manually manipulated relative to each other
by a person sitting in front of a computer 6 and visually observing the
jig models 38 and arthritic models 36 on the computer screen 9 and
manipulating the models 36, 38 by interacting with the computer controls
11. In one embodiment, by superimposing the jig models 38 (e.g., femur
and tibia arthroplasty jigs in the context of the joint being a knee)
over the arthroplasty target areas 42 of the arthritic models 36, or vice
versa, the surface models 40 of the arthroplasty target areas 42 can be
imported into the jig models 38, resulting in jig models 38 indexed to
matingly receive the arthroplasty target areas 42 of the arthritic models
36. Point W' (X0-k, Y0-k, Z0-k) can also be imported into
the jig models 38, resulting in jig models 38 positioned and oriented
relative to point W' (X0-k, Y0-k, Z0-k) to allow their
integration with the bone cut and drill hole data 44 of [block 125].

[0120]In one embodiment, the procedure for indexing the jig models 38 to
the arthroplasty target areas 42 is generally or completely automated, as
disclosed in U.S. patent application Ser. No. 11/959,344 to Park, which
is entitled System and Method for Manufacturing Arthroplasty Jigs, was
filed Dec. 18, 2007 and is incorporated by reference in its entirety into
this Detailed Description. For example, a computer program may create 3D
computer generated surface models 40 of the arthroplasty target areas 42
of the arthritic models 36. The computer program may then import the
surface models 40 and point W' (X0-k, Y0-k, Z0-k) into the
jig models 38, resulting in the jig models 38 being indexed to matingly
receive the arthroplasty target areas 42 of the arthritic models 36. The
resulting jig models 38 are also positioned and oriented relative to
point W' (X0-k, Y0-k, Z0-k) to allow their integration
with the bone cut and drill hole data 44 of [block 125].

[0121]In one embodiment, the arthritic models 36 may be 3D volumetric
models as generated from the closed-loop process discussed in U.S. patent
application Ser. No. 11/959,344 filed by Park. In other embodiments, the
arthritic models 36 may be 3D surface models as generated from the
open-loop process discussed in U.S. patent application Ser. No.
11/959,344 filed by Park.

[0122]In one embodiment, the models 40 of the arthroplasty target areas 42
of the arthritic models 36 may be generated via an overestimation process
as disclosed in U.S. Provisional Patent Application 61/083,053, which is
entitled System and Method for Manufacturing Arthroplasty Jigs Having
Improved Mating Accuracy, was filed by Park Jul. 23, 2008, and is hereby
incorporated by reference in its entirety into this Detailed Description.

[0123]As indicated in FIG. 1E, in one embodiment, the data regarding the
jig models 38 and surface models 40 relative to point W' (X0-k,
Y0-k, Z0-k) is packaged or consolidated as the "jig data" 46
[block 145]. The "jig data" 46 is then used as discussed below with
respect to [block 150] in FIG. 1E.

[0124]As can be understood from FIG. 1E, the "saw cut and drill hole data"
44 is integrated with the "jig data" 46 to result in the "integrated jig
data" 48 [block 150]. As explained above, since the "saw cut and drill
hole data" 44, "jig data" 46 and their various ancestors (e.g., 2D images
and femur and tibia data of blocks 110-125 and models 36, 38) are matched
to each other for position and orientation relative to point W and W',
the "saw cut and drill hole data" 44 is properly positioned and oriented
relative to the "jig data" 46 for proper integration into the "jig data"
46. The resulting "integrated jig data" 48, when provided to the CNC
machine 10, results in jigs 2: (1) configured to matingly receive the
arthroplasty target areas of the patient's bones; and (2) having cut
slots and drill holes that facilitate preparing the arthroplasty target
areas in a manner that allows the arthroplasty joint implants to
generally restore the patient's joint line to its pre-degenerated state
or natural alignment state.

[0125]As can be understood from FIGS. 1A and 1E, the "integrated jig data"
44 is transferred from the computer 6 to the CNC machine 10 [block 155].
Jig blanks 50 are provided to the CNC machine 10 [block 160], and the CNC
machine 10 employs the "integrated jig data" to machine the arthroplasty
jigs 2 from the jig blanks 50 [block 165].

[0127]As indicated in FIGS. 2A and 2B, a femur arthroplasty jig 2A may
include an interior side or portion 98 and an exterior side or portion
102. When the femur cutting jig 2A is used in a TKR procedure, the
interior side or portion 98 faces and matingly receives the arthroplasty
target area 42 of the femur lower end, and the exterior side or portion
102 is on the opposite side of the femur cutting jig 2A from the interior
portion 98.

[0128]The interior portion 98 of the femur jig 2A is configured to match
the surface features of the damaged lower end (i.e., the arthroplasty
target area 42) of the patient's femur 18. Thus, when the target area 42
is received in the interior portion 98 of the femur jig 2A during the TKR
surgery, the surfaces of the target area 42 and the interior portion 98
match.

[0129]The surface of the interior portion 98 of the femur cutting jig 2A
is machined or otherwise formed into a selected femur jig blank 50A and
is based or defined off of a 3D surface model 40 of a target area 42 of
the damaged lower end or target area 42 of the patient's femur 18.

[0130]As indicated in FIGS. 2C and 2D, a tibia arthroplasty jig 2B may
include an interior side or portion 104 and an exterior side or portion
106. When the tibia cutting jig 2B is used in a TKR procedure, the
interior side or portion 104 faces and matingly receives the arthroplasty
target area 42 of the tibia upper end, and the exterior side or portion
106 is on the opposite side of the tibia cutting jig 2B from the interior
portion 104.

[0131]The interior portion 104 of the tibia jig 2B is configured to match
the surface features of the damaged upper end (i.e., the arthroplasty
target area 42) of the patient's tibia 20. Thus, when the target area 42
is received in the interior portion 104 of the tibia jig 2B during the
TKR surgery, the surfaces of the target area 42 and the interior portion
104 match.

[0132]The surface of the interior portion 104 of the tibia cutting jig 2B
is machined or otherwise formed into a selected tibia jig blank 50B and
is based or defined off of a 3D surface model 40 of a target area 42 of
the damaged upper end or target area 42 of the patient's tibia 20.

[0133]While the discussion provided herein is given in the context of TKR
and TKR jigs and the generation thereof, the disclosure provided herein
is readily applicable to uni-compartmental or partial arthroplasty
procedures in the knee or other joint contexts. Thus, the disclosure
provided herein should be considered as encompassing jigs and the
generation thereof for both total and uni-compartmental arthroplasty
procedures.

[0134]The remainder of this Detailed Discussion will now focus on various
embodiments for performing POP.

[0135]B. Overview of Preoperative Planning ("POP") Procedure

[0136]In one embodiment, as can be understood from [blocks 100-110] of
FIGS. 1B-1C2, medical images 16 of the femur and tibia 18, 20 are
generated [Blocks 100 and 105] and coronal, axial and sagittal image
slices are analyzed to determine reference data 28, 100, 900. [Block
115]. The sizes of the implant models 34 are selected relative to the
femur and tibia reference data. [Block 112, 114 and 121, 122]. The
reference data 28, 100, 900 is utilized with the data associated with
implant models 34 to determine the cut plane location. The joint spacing
between the femur and the tibia is determined. An adjustment value tr is
determined to account for cartilage thickness or joint gap of a restored
joint. The implant models 34 are shifted or adjusted according to the
adjustment value tr [blocks 118 and 123]. Two dimensional computer
implant models 34 are rendered into the two dimensional imaging slice(s)
of the bones 28 such that the 2D implant models 34 appear along side the
2D imaging slices of the bones 28. In one embodiment, ITK software,
manufactured by Kitware, Inc. of Clifton Park, N.Y. is used to perform
this rendering. Once the 2D implant models 34 are rendered into the
MRI/CT image, the proper selection, orientation and position of the
implant models can be verified. An additional verification process may be
used wherein 3D models of the bones and implants are created and proper
positioning of the implant may be verified. Two dimensional computer
models 34 and three dimensional computer models 1004, 1006 of the femur
and tibia implants are generated from engineering drawings of the
implants and may be generated via any of the above-referenced 2D and 3D
modeling programs to confirm planning. If the implant sizing is not
correct, then the planning will be amended by further analysis of the 2D
images. If the implant sizing is accurate, then planning is complete. The
process then continues as indicated in [block 125] of FIG. 1E.

[0137]This ends the overview of the POP process. The following discussions
will address each of the aspects of the POP process in detail.

[0138]C. Femur and Tibia Images

[0139]FIG. 3A depicts 2D bone models or images 28', 28'' of the femur and
tibia 18, 20 from medical imaging scans 16. While FIG. 3A represents the
patient's femur 18 and tibia 20 prior to injury or degeneration, it can
be understood that, in other embodiments, the images 28', 28'' may also
represent the patient's femur 18 and tibia 20 after injury or
degeneration. More specifically, FIG. 3A is a 2D image slice 28' of a
femur lower end 200 and an 2D image slice 28'' of a tibia upper end 205
representative of the corresponding patient bones 18, 20 in a
non-deteriorated state and in position relative to each to form a knee
joint 14. The femur lower end 200 includes condyles 215, and the tibia
upper end 205 includes a plateau 220. The images or models 28', 28'' are
positioned relative to each other such that the curved articular surfaces
of the condyles 215, which would normally mate with complementary
articular surfaces of the plateau 220, are instead not mating, but
roughly positioned relative to each other to generally approximate the
knee joint 14.

[0140]As generally discussed above with respect to FIGS. 1A-1C2, the POP
begins by using a medical imaging process, such as magnetic resonance
imaging (MRI), computed tomography (CT), and/or another other medical
imaging process, to generate imaging data of the patient's knee. For
example, current commercially available MRI machines use 8 bit (255
grayscale) to show the human anatomy. Therefore, certain components of
the knee, such as the cartilage, cortical bone, cancellous bone,
meniscus, etc., can be uniquely viewed and recognized with 255 grayscale.
The generated imaging data is sent to a preoperative planning computer
program. Upon receipt of the data, a user or the computer program may
analyze the data (e.g., two-dimensional MRI images 16, and more
specifically, the 2D femur image(s) 28' or 2D tibia image(s) 28'') to
determine various reference points, reference lines and reference planes.
In one embodiment, the MRI imaging scans 16 may be analyzed and the
reference data for POP may be generated by a proprietary software program
called PerForm.

[0141]For greater detail regarding the methods and systems for computer
modeling joint bones, such as the femur and tibia bones forming the knee,
please see the following U.S. patent applications, which are all
incorporated herein in their entireties: U.S. patent application Ser. No.
11/656,323 to Park et al., titled "Arthroplasty Devices and Related
Methods" and filed Jan. 19, 2007; U.S. patent application Ser. No.
10/146,862 to Park et al., titled "Improved Total Joint Arthroplasty
System" and filed May 15, 2002; U.S. patent Ser. No. 11/642,385 to Park
et al., titled "Arthroplasty Devices and Related Methods" and filed Dec.
19, 2006.

[0142]FIG. 3B is an isometric view of a computer model of a femur implant
34' and a computer model of a tibia implant 34'' in position relative to
each to form an artificial knee joint 14. The computer models 34', 34''
may be formed, for example, via computer aided drafting or 3D modeling
programs. As will be discussed later in this detailed description, the
implant computer models may be in 2D or in 3D as necessary for the
particular planning step.

[0143]The femur implant model 34' will have a joint side 240 and a bone
engaging side 245. The joint side 240 will have a condyle-like surface
for engaging a complementary surface of the tibia implant model 34''. The
bone engaging side 245 will have surfaces and engagement features 250 for
engaging the prepared (i.e., sawed to shape) lower end of the femur 18.

[0144]The tibia implant model 34'' will have a joint side 255 and a bone
engaging side 260. The joint side 255 will have a plateau-like surface
configured to engage the condyle-like surface of the femur implant model
34'. The bone engaging side 260 will have an engagement feature 265 for
engaging the prepared (i.e., sawed to shape) upper end of the tibia 20.

[0145]As discussed in the next subsections of this Detailed Description,
the reference data of the femur and tibia bone models or images 28', 28''
may be used in conjunction with the implant models 34', 34'' to select
the appropriate sizing for the implants actually to be used for the
patient. The resulting selections can then be used for planning purposes,
as described later in this Detailed Description.

[0146]D. Femur Planning Process

[0147]For a discussion of the femur planning process, reference is now
made to FIGS. 4-22. FIGS. 4-9 illustrate a process in the POP wherein the
system 4 utilizes 2D imaging slices (e.g., MRI slices, CT slices, etc.)
to determine femur reference data, such as reference points, lines and
planes via their relationship to the trochlear groove plane-GHO of the
femur. The resulting femur reference data 100 is then mapped or projected
to a y-z coordinate system (sagittal plane). The femur reference data is
then applied to a candidate femur implant model, resulting in femoral
implant reference data 100'. The data 100, 100' is utilized to select an
appropriate set of candidate implants, from which a single candidate
implant will be chosen, which selection will be discussed in more detail
below with reference to FIGS. 10-22.

[0148]1. Determining Femur Reference Data

[0149]For a discussion of a process used to determine the femur reference
data, reference is now made to FIGS. 4-7C. FIG. 4 is a perspective view
of the distal end of a 3D model 1000 of the femur image of FIG. 3A
wherein the femur reference data 100 is shown. As will be explained in
more detail below, the femur reference data is generated by an analysis
of the 2D image scans and FIG. 4 depicts the relative positioning of the
reference data on a 3D model. As shown in FIG. 4, the femur reference
data 100 may include reference points (e.g. D1, D2), reference
lines (e.g. GO, EF) and reference planes (e.g. P, S). The femur reference
data 100 may be determined by a process illustrated in FIGS. 5A-7D and
described in the next sections.

[0150]As shown in FIG. 5A, which is a sagittal view of a femur 18
illustrating the orders and orientations of imaging slices 16 that are
utilized in the femur POP, a multitude of image slices may be compiled.
In some embodiments, the image slices may be analyzed to determine, for
example, distal contact points prior to or instead of being compiled into
a bone model. Image slices may extend medial-lateral in planes that would
be normal to the longitudinal axis of the femur, such as image slices 1-5
of FIGS. 5A and 6D. Image slices may extend medial-lateral in planes that
would be parallel to the longitudinal axis of the femur, such as image
slices 6-9 of FIGS. 5A and 7B. The number of image slices may vary from
1-50 and may be spaced apart in a 2 mm spacing or other spacing.

[0151]a. Determining Reference Points P1P2

[0152]In some embodiments, the planning process begins with the analysis
of the femur slices in a 2D axial view. As can be understood from FIG.
5B, which depicts axial imaging slices of FIG. 5A, the series of 2D axial
femur slices are aligned to find the most posterior point of each
condyle. For example, the most posterior points of slice 5, P1A,
P2A, are compared to the most posterior points of slice 4, P1B,
P2B. The most posterior points of slice 4 are more posterior than
those of slice 5. Therefore, the points of slice 4 will be compared to
slice 3. The most posterior points of slice 3, P1C, P2C, are
more posterior than the posterior points P1B, P2B of slice 4.
Therefore, the points of slice 3 will be compared to slice 2. The most
posterior points of slice 2, P1D, P2D, are more posterior than
the posterior points P1C, P2C of slice 3. Therefore, the points
of slice 2 will be compared to slice 1. The most posterior points of
slice 1, P1E, P2E, are more posterior than the posterior points
P1D, P2D of slice 2. In some embodiments, the points of slice 1
may be compared to slice 0 (not shown). The most posterior points of
slice 0, P1F, P2F, are less posterior than the posterior points
P1E, P2E of slice 1. Therefore, the points of slice 1 are
determined to be the most posterior points P1, P2 Of the femur.
In some embodiments, points P1 and P2 may be found on different
axial slices. That is, the most posterior point on the medial side and
most posterior point on the lateral side may lie in different axial
slices. For example, slice 2 may include the most posterior point on the
lateral side, while slice 1 may include the most posterior point on the
medial side. It can be appreciated that the number of slices that are
analyzed as described above may be greater than five slices or less than
five slices. The points P1, P2 are stored for later analysis.

[0153]b. Determining Reference Points D1D2

[0154]The planning process continues with the analysis of the femur slices
in a 2D coronal view. As can be understood from FIG. 5C, which depicts
coronal imaging slices of FIG. 5A, the series of 2D coronal femur slices
are aligned to find the most distal point of each condyle. For example,
the most distal points of slice 6, D1A, D2A, are compared to
the most distal points of slice 7, D1B, D2B. The most distal
points of slice 7 are more distal than those of slice 6. Therefore, the
points of slice 7 will be compared to slice 8. The most distal points of
slice 8, D1C, D2C, are more distal than the distal points
D1B, D2B of slice 7. Therefore, the points of slice 8 will be
compared to slice 9. The most distal points of slice 9, D1D,
D2D, are more distal than the distal points D1C, D2C of
slice 8. In some embodiments, the points of slice 9 may be compared to
slice 10 (not shown). The most distal points of slice 10, D1E,
D2E, are less distal than the distal points D1D, D2D of
slice 9. Therefore, the points of slice 9 are determined to be the most
distal points D1, D2 of the femur. In some embodiments, points
D1 and D2 may be found on different coronal slices. That is,
the most distal point on the medial side and most distal point on the
lateral side may lie in different coronal slices. For example, slice 9
may include the most distal point on the lateral side, while slice 8 may
include the most distal point on the medial side. It can be appreciated
that the number of slices that are analyzed as described above may be
greater than four slices or less than four slices. The points D1,
D2 are stored for future analysis.

[0155]c. Determining Reference Lines CD and GO

[0156]Analysis of the 2D slices in the axial view aid in the determination
of internal/external rotation adjustment. The points D1, D2
represent the lowest contact points of each of the femoral lateral and
medial condyles 302, 303. Thus, to establish an axial-distal reference
line, line CD, in 2D image slice(s), the analysis utilizes the most
distal point, either D1 or D2, from the undamaged femoral
condyle. For example, as shown in FIG. 6A, which is an axial imaging
slice of the femur of FIG. 5A, when the lateral condyle 302 is undamaged
but the medial condyle 303 is damaged, the most distal point D1 will
be chosen as the reference point in establishing the axial-distal
reference line, line CD. The line CD is extended from the lateral edge of
the lateral condyle, through point D1, to the medial edge of the
medial condyle. If the medial condyle was undamaged, then the distal
point D2 would be used as the reference point through which line CD
would be extended. The distal points D1, D2 and line CD are
stored for later analysis.

[0157]A line CD is verified. A most distal slice of the series of axial
views is chosen to verify the position of an axial-distal reference line,
line CD. As shown in FIG. 6A, the most distal slice 300 of the femur
(e.g., slice 5 in FIGS. 5A and 6D) is chosen to position line CD such
that line CD is generally anteriorly-posteriorly centered in the lateral
and medial condyles 302, 303. Line CD is generally aligned with the
cortical bone of the undamaged posterior condyle. For example, if the
medial condyle 303 is damaged, the line CD will be aligned with the
undamaged lateral condyle, and vise versa. To verify the location of line
CD and as can be understood from FIGS. 4 and 6C, the line CD will also
connect the most distal points D1, D2. The geography
information of line CD will be stored for future analysis.

[0158]Line GO is determined. The "trochlear groove axis" or the "trochlear
groove reference plane" is found. In the knee flexion/extension motion
movement, the patella 304 generally moves up and down in the femoral
trochlear groove along the vertical ridge and generates quadriceps forces
on the tibia. The patellofemoral joint and the movement of the femoral
condyles play a major role in the primary structure and mechanics across
the joint. In a normal knee model or properly aligned knee, the vertical
ridge of the posterior patella is generally straight (vertical) in the
sliding motion. For the OA patients' knees, there is rarely bone damage
in the trochlear groove; there is typically only cartilage damage.
Therefore, the trochlear groove of the distal femur can serve as a
reliable bone axis reference. In relation to the joint line assessment,
as discussed with reference to FIGS. 14A-14J, the trochlear groove axis
of the distal femur is perpendicular or nearly perpendicular to the joint
line of the knee. A detailed discussion of the trochlear groove axis or
the trochlear groove reference plane may be found in co-owned U.S. patent
application Ser. No. 12/111,924, which is incorporated by reference in
its entirety.

[0159]To perform the trochlear groove analysis, the MRI slice in the axial
view with the most distinct femoral condyles (e.g., the slice with the
largest condyles such as slice 400 of FIG. 6B) will be chosen to position
the trochlear groove bisector line, line TGB. As shown in FIG. 6B, which
is an axial imaging slice of the femur of FIG. 5A, the most distinct
femoral condyles 302, 303 are identified. The trochlear groove 405 is
identified from image slice 400. The lowest extremity 406 of the
trochlear groove 405 is then identified. Line TGB is then generally
aligned with the trochlear groove 405 across the lowest extremity 406. In
addition, and as shown in FIG. 6D, which is the axial imaging slices 1-5
taken along section lines 1-5 of the femur in FIG. 5A, each of the slices
1-5 can be aligned vertically along the trochlear groove 405, wherein
points G1, G2, G3, G4, G5 respectively represent the lowest extremity 406
of trochlear groove 405 for each slice 1-5. By connecting the various
points G1, G2, G3, G4, G5, a point O can be obtained. As can be
understood from FIGS. 4 and 6C, resulting line GO is perpendicular or
nearly perpendicular to line D1D2. In a 90° knee
extension, line GO is perpendicular or nearly perpendicular to the joint
line of the knee and line P1P2. Line GO is stored for later
analysis.

[0160]d. Determining Reference Lines EF and HO

[0161]Analysis of the 2D slices in the coronal view aid in the
determination of femoral varus/valgus adjustment. The points P1,
P2 determined above represent the most posterior contact points of
each of the femoral lateral and medial condyles 302, 303. Thus, to
establish a coronal posterior reference line, line EF, in 2D image
slice(s), the analysis utilizes the most posterior point, either P1
or P2, from the undamaged femoral condyle. For example, as shown in
FIG. 7A, when the lateral condyle 302 is undamaged but the medial condyle
303 is damaged, the most posterior point P1 will be chosen as the
reference point in establishing the coronal posterior reference line,
line EF. The line EF is extended from the lateral edge of the lateral
condyle, through point P1, to the medial edge of the medial condyle.
If the medial condyle was undamaged, then the posterior point P2
would be used as the reference point through which line EF would be
extended. The posterior points P1, P2 and line EF are stored
for later analysis.

[0162]The points, P1P2 were determined as described above with
reference to FIG. 5B. Line EF is then verified. A most posterior slice of
the series of coronal views is chosen to verify the position of a coronal
posterior reference line, line EF. As shown in FIG. 7A, which is a
coronal imaging slice of FIG. 5A, the most posterior slice 401 of the
femur (e.g., slice 6 in FIGS. 5A and 7B) is chosen to position line EF
such that line EF is generally positioned in the center of the lateral
and medial condyles 302, 303. Line EF is generally aligned with the
cortical bone of the undamaged posterior condyle. For example, if the
medial condyle 303 is damaged, the line EF will be aligned with the
undamaged lateral condyle, and vise versa. To verify the location of line
EF and as can be understood from FIG. 4, the line EF will also connect
the most posterior points P1, P2. The geography information of
line EF will be stored for future analysis.

[0163]In some embodiments, line HO may be determined. As shown in FIG. 7B,
which are coronal imaging slices 6-9 taken along section lines 6-9 of the
femur in FIG. 5A, each of the image slices 6-9 taken from FIG. 5A can be
aligned along the trochlear groove. The points H6, H7, H8, H9
respectively represent the lowest extremity of the trochlear groove for
each of the image slices 6-8 from FIG. 5A. By connecting the various
points H6, H7, H8, the point O can again be obtained. The resulting line
HO is established as the shaft reference line-line SHR. The
coronal-posterior reference line, line EF and coronal-distal reference
line, line AB may be adjusted to be perpendicular or nearly perpendicular
to the shaft reference line-line SHR (line HO). Thus, the shaft reference
line, line SHR (line HO) is perpendicular or nearly perpendicular to the
coronal-posterior reference line, line EF and to the coronal-distal
reference line, line AB throughout the coronal image slices.

[0164]As can be understood from FIGS. 4 and 7B, the trochlear groove
plane-GHO, as the reference across the most distal extremity of the
trochlear groove of the femur and in a 90° knee extension, should
be perpendicular to line AB. The line-HO, as the reference across the
most posterior extremity of trochlear groove of the femur and in a
0° knee extension, should be perpendicular to line AB.

[0165]e. Determining Reference Line AB and Reference Planes P and S

[0166]As can be understood from FIG. 4, a posterior plane S may be
constructed such that the plane S is normal to line GO and includes
posterior reference points P1, P2. A distal plane P may be constructed
such that it is perpendicular to posterior plane S and may include distal
reference points D1, D2 (line CD). Plane P is perpendicular to plane S
and forms line AB therewith. Line HO and line GO are perpendicular or
nearly perpendicular to each other. Lines CD, AB and EF are parallel or
nearly parallel to each other. Lines CD, AB and EF are perpendicular or
nearly perpendicular to lines HO and GO and the trochlear plane GHO.

[0167]f. Verification of the Femoral Reference Data

[0168]As shown in FIG. 7C, which is an imaging slice of the femur of FIG.
5A in the sagittal view, after the establishment of the reference lines
from the axial and coronal views, the axial-distal reference line CD and
coronal-posterior reference line EF and planes P, S are verified in the
2D sagittal view. The sagittal views provide the extension/flexion
adjustment. Thus, as shown in FIG. 7C, slice 800 shows a sagittal view of
the femoral medial condyle 303. Line-bf and line-bd intersect at point-b.
As can be understood from FIGS. 4 and 7C, line-bf falls on the coronal
plane-S, and line-bd falls on the axial plane-P. Thus, in one embodiment
of POP planning, axial and coronal views are used to generate
axial-distal and coronal-posterior reference lines CD, EF. These two
reference lines CD, EF can be adjusted (via manipulation of the reference
data once it has been imported and opened on the computer) to touch in
the black cortical rim of the femur. The adjustment of the two reference
lines on the femur can also be viewed simultaneously in the sagittal view
of the MRI slice, as displayed in FIG. 7C. Thus, the sagittal view in
FIG. 7C provides one approach to verify if the two reference lines do
touch or approximately touch with the femur cortical bone. In some
embodiments, line-bf is perpendicular or nearly perpendicular to line-bd.
In other embodiments, line bf may not be perpendicular to bd. This angle
depends at least partially on the rotation of femoral bone within MRI.

[0169]With reference to FIGS. 4-7C, in one embodiment, lines HO and GO may
be within approximately six degrees of being perpendicular with lines
P1P2, D1D2 and A1A2 or the preoperative
planning for the distal femur will be rejected and the above-described
processes to establish the femoral reference data 100 (e.g. reference
lines CD, EF, AB, reference points P1P2, D1D2) will
be repeated until the femoral reference data meets the stated tolerances,
or a manual segmentation for setting up the reference lines will be
performed. In other embodiments, if there are multiple failed attempts to
provide the reference lines, then the reference data may be obtained from
another similar joint that is sufficiently free of deterioration. For
example, in the context of knees, if repeated attempts have been made
without success to determined reference data in a right knee medial femur
condyle based on data obtained from the right knee lateral side, then
reference data could be obtained from the left knee lateral or medial
sides for use in the determination of the femoral reference data.

[0170]g. Mapping the Femoral Reference Data to a y-z Plane

[0171]As can be understood from FIGS. 7D-9, the femoral reference data 100
will be mapped to a y-z coordinate system to aid in the selection of an
appropriate implant. As shown in FIGS. 7D-7E, which are axial and coronal
slices, respectively, of the femur, the points D1D2 of the
distal reference line D1D2 or CD were determined from both a 2D
axial view and a 2D coronal view and therefore are completely defined in
3D. Similarly, the points P1P2 of the posterior reference line
P1P2 or EF were determined from both a 2D axial view and a 2D
coronal view and therefore are completely defined in 3D.

[0172]As shown in FIG. 8, which is a posterior view of a femur 3D model
1000, the reference data 100 determined by an analysis of 2D images may
be imported onto a 3D model of the femur for verification purposes. The
distance L between line EF and line CD can be determined and stored for
later analysis during the selection of an appropriate implant size.

[0173]As indicated in FIG. 9, which depicts a y-z coordinate system, the
posterior points P1P2 and distal points D1D2 of the
2D images 28' may also be projected onto a y-z plane and this information
is stored for later analysis.

[0174]2. Determining Femoral Implant Reference Data

[0175]There are 6 degrees of freedom for a femoral implant to be moved and
rotated for placement on the femoral bone. The femur reference data 100
(e.g. points P1P2, D1D2, reference lines EF, CD,
reference planes P, S) is utilized in the selection and placement of the
femoral implant. For a discussion of a process used to determine the
implant reference data, reference is now made to FIGS. 10-22.

[0177]As shown in FIGS. 10 and 11, which are perspective views of a
femoral implant model 34', the femur reference data 100 may be mapped to
a 3D model of the femur implant model 34' in a process of POP. The femur
reference data 100 and the femur implant model 34' are opened together.
The femur implant model 34' is placed on a 3D coordinate system and the
data 100 is also transferred to that coordinate system thereby mapping
the data 100 to the model 34' to create femoral implant data 100'. The
femoral implant data 100' includes an axial-distal reference line
(line-C'D') and a coronal-posterior reference line (line-E'F').

[0178]As can be understood from FIGS. 10 and 11, distal
line-D1'D2' represents the distance between the two most distal
points D1', D2'. Posterior line-P1'P2' represents the
distance between the two most posterior points P1', P2'. The
lines-D1'D2', P1'P2' of the implant model 34' can be
determined and stored for further analysis.

[0179]As shown in FIG. 12, which shows a coordinate system wherein some of
the femoral implant reference data 100' is shown, the endpoints
D1'D2' and P1'P2' may also be projected onto a y-z
plane and this information is stored for later analysis. As shown in FIG.
13, the implant reference data 100' may also be projected onto the
coordinate system. The distance L' between line E'F' and line C'D', and
more specifically between lines D1'D2', P1'P2', can
be determined and stored for later use during the selection of an
implant.

[0180]3. Determining Joint Line and Adjustment to Implant That Allows
Condylar Surfaces of Implant Model to Restore Joint to Natural
Configuration

[0181]In order to allow an actual physical arthroplasty implant to restore
the patient's knee to the knee's pre-degenerated or natural configuration
with the natural alignment and natural tensioning in the ligaments, the
condylar surfaces of the actual physical implant generally replicate the
condylar surfaces of the pre-degenerated joint bone. In one embodiment of
the systems and methods disclosed herein, condylar surfaces of the 2D
implant model 34' are matched to the condylar surfaces of the 2D bone
model or image 28'. However, because the bone model 28' may be bone only
and not reflect the presence of the cartilage that actually extends over
the pre-degenerated condylar surfaces, the alignment of the implant 34'
may be adjusted to account for cartilage or proper spacing between the
condylar surfaces of the cooperating actual physical implants (e.g., an
actual physical femoral implant and an actual physical tibia implant)
used to restore the joint such that the actual physical condylar surfaces
of the actual physical cooperating implants will generally contact and
interact in a manner substantially similar to the way the cartilage
covered condylar surfaces of the pre-degenerated femur and tibia
contacted and interacted. Thus, in one embodiment, the implant models are
modified or positionally adjusted to achieve the proper spacing between
the femur and tibia implants.

[0182]a. Determine Adjustment Value tr

[0183]To achieve the correct adjustment, an adjustment value tr may be
determined. In one embodiment, the adjustment value tr may be determined
in 2D by a calipers measuring tool (a tool available as part of the
software). The calipers tool is used to measure joint spacing between the
femur and the tibia by selection of two points in any of the 2D MRI views
and measuring the actual distance between the points. In another
embodiment, the adjustment value tr that is used to adjust the implant
during planning may be based off of an analysis associated with cartilage
thickness. In another embodiment, the adjustment value tr used to adjust
the implant during planning may be based off of an analysis of proper
joint gap spacing. Both the cartilage thickness and joint gap spacing
methods are discussed below in turn.

[0184]i. Determining Cartilage Thickness and Joint Line

[0185]FIG. 14A shows the femoral condyle 310 and the proximal tibia of the
knee in a sagittal MRI image slice. The distal femur 28' is surrounded by
the thin black rim of cortical bone. Due to the nature of irregular bone
and cartilage loss in OA patients, it can be difficult to find the proper
joint line reference for the models used during the POP.

[0186]The space between the elliptical outlining 325', 325'' along the
cortical bone represents the cartilage thickness of the femoral condyle
310. The ellipse contour of the femoral condyle 310 can be seen on the
MRI slice shown in FIG. 14A and obtained by a three-point tangent contact
spot (i.e., point t1, t2, t3) method. In a normal, healthy knee, the bone
joint surface is surrounded by a layer of cartilage. Because the
cartilage is generally worn-out in OA and the level of cartilage loss
varies from patient to patient, it may be difficult to accurately account
for the cartilage loss in OA patients when trying to restore the joint
via TKA surgery. Therefore, in one embodiment of the methodology and
system disclosed herein, a minimum thickness of cartilage is obtained
based on medical imaging scans (e.g., MRI, etc.) of the undamaged
condyle. Based on the cartilage information, the joint line reference can
be restored. For example, the joint line may be line 630 in FIG. 14B.

[0187]The system and method disclosed herein provides a POP method to
substantially restore the joint line back to a "normal or natural knee"
status (i.e., the joint line of the knee before OA occurred) and
preserves ligaments in TKA surgery (e.g., for a total knee arthroplasty
implant) or partial knee arthroplasty surgery (e.g., for a uni-knee
implant).

[0188]FIG. 14B is a coronal view of a knee model in extension. As depicted
in FIG. 14B, there are essentially four separate ligaments that stabilize
the knee joint, which are the medial collateral ligament (MCL), anterior
cruciate ligament (ACL), lateral collateral ligament (LCL), and posterior
cruciate ligament (PCL). The MCL and LCL lie on the sides of the joint
line and serve as stabilizers for the side-to-side stability of the knee
joint. The MCL is a broader ligament, whereas the LCL is a distinct
cord-like structure.

[0189]The ACL is located in the front part of the center of the joint. The
ACL is a very important stabilizer of the femur on the tibia and serves
to prevent the tibia from rotating and sliding forward during agility,
jumping, and deceleration activities. The PCL is located directly behind
the ACL and serves to prevent the tibia from sliding to the rear. The
system and method disclosed herein provides POP that allows the
preservation of the existing ligaments without ligament release during
TKA surgery. Also, the POP method provides ligament balance, simplifying
TKA surgery procedures and reducing pain and trauma for OA patients.

[0190]As indicated in FIG. 14B, the joint line reference 630 is defined
between the two femoral condyles 302, 303 and their corresponding tibia
plateau regions 404, 406. Area A illustrates a portion of the lateral
femoral condyle 302 and a portion of the corresponding lateral plateau
404 of tibia 205. Area B illustrates the area of interest showing a
portion of the medial femoral condyle 303 and a portion of the
corresponding medial plateau 406 of tibia 205.

[0191]FIGS. 14C, 14D and 14F illustrate MRI segmentation slices for joint
line assessment. FIG. 14E is a flow chart illustrating the method for
determining cartilage thickness used to determine proper joint line. The
distal femur 200 is surrounded by the thin black rim of cortical bone
645. The cancellous bone (also called trabecular bone) 650 is an inner
spongy structure. An area of cartilage loss 655 can be seen at the
posterior distal femur. For OA patients, the degenerative cartilage
process typically leads to an asymmetric wear pattern that results in one
femoral condyle with significantly less articulating cartilage than the
other femoral condyle. This occurs when one femoral condyle is overloaded
as compared to the other femoral condyle.

[0192]As can be understood from FIGS. 14C, 14E and 14F, the minimum
cartilage thickness is observed and measured for the undamaged and
damaged femoral condyle 302, 303 [block 1170]. If the greatest cartilage
loss is identified on the surface of medial condyle 303, for example,
then the lateral condyle 302 can be used as the cartilage thickness
reference for purposes of POP. Similarly, if the greatest cartilage loss
is identified on the lateral condyle 302, then the medial condyle 303 can
be used as the cartilage thickness reference for purposes of POP. In
other words, use the cartilage thickness measured for the least damaged
condyle cartilage as the cartilage thickness reference for POP[block
1175].

[0193]As indicated in FIG. 14D, the thickness of cartilage can be analyzed
in order to restore the damaged knee compartment back to its pre-OA
status. In each of the MRI slices taken in regions A and B in FIG. 14B,
the reference lines as well as the major and minor axes 485, 490 of
ellipse contours 480', 480'' in one femoral condyle 303 can be obtained.

[0194]As shown in FIG. 14F, for the three-point method, the tangents are
drawn on the condylar curve at zero degrees and 90 degrees articular
contact points. The corresponding tangent contact spots t1 and t2 are
obtained from the tangents. The line 1450 perpendicular to the line 1455
determines the center of the ellipse curve, giving the origin of (0, 0).
A third tangent contact spot t3 can be obtained at any point along the
ellipse contour between the zero degree, t1 point and the 90 degree, t2
point. This third spot t3 can be defined as k, where k=1 to n points.

[0195]The three-point tangent contact spot analysis may be employed to
configure the size and radius of the condyle 303 of the femur bone model
28'. This provides the "x" coordinate and "y" coordinate, as the (x, y)
origin (0, 0) shown in FIG. 14D. The inner ellipse model 480' of the
femoral condyle shows the femoral condyle surrounded by cortical bone
without the cartilage attached. The minimum cartilage thickness
tmmin outside the inner ellipse contour 480' is measured. Based on
the analysis of the inner ellipse contour 480' (i.e., the bone surface)
and outer ellipse contour 480'' (i.e., the cartilage surface) of the one
non-damaged condyle of the femur bone model 28', the inner ellipse
contour 480' (i.e., the bone surface) and the outer ellipse contour 480''
(i.e., the cartilage surface) of the other condyle (i.e., the damage or
deteriorated condyle) may be determined.

[0196]As can be understood from FIGS. 14B and 14D, ellipse contours 480',
480'' are determined in areas A and B for the condyles 302, 303 of the
femur bone model 28'. The inner ellipse contour 480', representing the
bone-only surface, and the outer ellipse contour 480'', representing the
bone-and-cartilage surface, can be obtained. The minimum cartilage
thickness tmmin is measured based on the cartilage thickness tr
between the inner ellipse 480' and outer ellipse 480''. MRI slices of the
two condyles 302, 303 of the femur bone model 28' in areas A and B are
taken to compare the respective ellipse contours in areas A and B. If the
cartilage loss is greatest at the medial condyle 303 in the MRI slices,
the minimum thickness tmmin for the cartilage can be obtained from
the lateral condyle 302. Similarly, if the lateral condyle 302 has the
greatest cartilage loss, the cartilage thickness tmmin can be
obtained from undamaged medial condyle 303 of the femur restored bone
model 28'. The minimum cartilage can be illustrated in the formula,
tmmin=MIN (ti), where i=1 to k.

[0197]ii. Determining Joint Gap

[0198]As mentioned above, in one embodiment, the adjustment value tr may
be determined via a joint line gap assessment. The gap assessment may
serve as a primary estimation of the gap between the distal femur and
proximal tibia of the bone images. The gap assessment may help achieve
proper ligament balancing.

[0199]In one embodiment, an appropriate ligament length and joint gap may
not be known from the 2D bone models or images 28', 28'' (see, e.g. FIG.
3B) as the bone models or images may be oriented relative to each other
in a fashion that reflects their deteriorated state. For example, as
depicted in FIG. 14J, which is a coronal view of bone models 28', 28''
oriented (e.g., tilted) relative to each other in a deteriorated state
orientation, the lateral side 1487 was the side of the deterioration and,
as a result, has a greater joint gap between the distal femur and the
proximal tibia than the medial side 1485, which was the non-deteriorated
side of the joint in this example.

[0200]In one embodiment, ligament balancing may also be considered as a
factor for selecting the appropriate implant size. As can be understood
from FIG. 14J, because of the big joint gap in the lateral side 1487, the
presumed lateral ligament length (L1+L2+L3) may not be reliable to
determine proper ligament balancing. However, the undamaged side, which
in FIG. 14J is the medial side 1485, may be used in some embodiments as
the data reference for a ligament balancing approach. For example, the
medial ligament length (M1+M2+M3) of the undamaged medial side 1485 may
be the reference ligament length used for the ligament balancing approach
for implant size selection.

[0201]In one embodiment of the implant size selection process, it may be
assumed that the non-deteriorated side (i.e., the medial side 1485 in
FIG. 14J in this example) may have the correct ligament length for proper
ligament balancing, which may be the ligament length of (M1+M2+M3). When
the associated ligament length ("ALL") associated with a selected implant
size equals the correct ligament length of (M1+M2+M3), then the correct
ligament balance is achieved, and the appropriate implant size has been
selected. However, when the ALL ends up being greater than the correct
ligament length (M1+M2+M3), the implant size associated with the ALL may
be incorrect and the next larger implant size may need to be selected for
the design of the arthroplasty jig 2.

[0202]For a discussion regarding the gap assessment, which may also be
based on ligament balance off of a non-deteriorated side of the joint,
reference is made to FIGS. 14G and 14H. FIGS. 14G and 14H illustrate
coronal views of the bone models 28', 28'' in their post-degeneration
alignment relative to each as a result of OA or injury. As shown in FIG.
14G, the tibia model 28'' is tilted away from the lateral side 1487 of
the knee 1486 such that the joint gap between the femoral condylar
surfaces 1490 and the tibia condylar surfaces 1491 on the lateral side
1487 is greater than the joint gap on the medial side 1485.

[0203]As indicated in FIG. 14H, which illustrates the tibia in a coronal
cross section, the line 1495 may be employed to restore the joint line of
the knee 1486. The line 1495 may be caused to extend across each of
lowest extremity points 1496, 1497 of the respective femoral lateral and
medial condyles 1498, 1499. In this femur bone model 28', line 1495 may
be presumed to be parallel or nearly parallel to the joint line of the
knee 1486.

[0204]As illustrated in FIG. 14H, the medial gap Gp2 represents the
distance between the distal femoral medial condyle 1499 and the proximal
tibia medial plateau 1477. The lateral gap Gp1 represents the distance
between the distal femoral lateral condyle 1498 and the proximal tibia
lateral plateau 1478. In this example illustrated in FIG. 14H, the
lateral gap Gp1 is significantly larger than the medial gap Gp2 due to
degeneration caused by injury, OA, or etc., that occurred in the lateral
side 1487 of the knee 1486. It should be noted that the alignment of the
bone models 28', 28'' relative to each other for the example illustrated
in FIGS. 14G and 14H depict the alignment the actual bones have relative
to each other in a deteriorated state. To restore the joint line
reference and maintain ligament balancing for the medial collateral
ligament (MCL) and lateral collateral ligament (LCL), the joint line gap
Gp3 that is depicted in FIG. 14I, which is the same view as FIG. 14G,
except with the joint line gap Gp3 in a restored state, may be used for
the joint spacing compensation adjustment as described below. As
illustrated in FIG. 14I, the lines 1495 and 1476 respectively extend
across the most distal contact points 1496, 1497 of the femur condyles
1498, 1499 and the most proximal contact points 1466, 1467 of the tibia
plateau condyles 1477, 1478.

[0205]For calculation purposes, the restored joint line gap Gp3 may be
which ever of Gp1 and Gp2 has the minimum value. In other words, the
restored joint line gap Gp3 may be as follows: Gp3=MIN (Gp1, Gp2). For
purposes of the adjustment for joint spacing compensation, the adjustment
value tr may be calculated as being half of the value for Gp3, or in
other words, tr=Gp3/2. As can be understood from FIGS. 14G-14H and 14J,
in this example, the non-deteriorated side 1485 has Gp2, which is the
smallest joint line gap and, therefore, Gp3=Gp2 in the example depicted
in FIG. 14G-14J, and tr=Gp2/2.

[0206]In one embodiment, the joint line gap assessment may be at least a
part of a primary assessment of the geometry relationship between the
distal femur and proximal tibia. In such an embodiment, the joint gap
assessment step may occur prior to the femur planning steps of the POP
process. However, in other embodiments, the joint line gap assessment may
occur at other points along the overall POP process.

[0207]b. Determine Compensation for Joint Spacing

[0208]Once the adjustment value tr is determined based off of cartilage
thickness or joint line gap Gp3, the planning for the femoral implant
model 34' can be modified or adjusted to compensate for the joint spacing
in order to restore the joint line. As shown in FIG. 15, which is a 3D
coordinate system wherein the femur reference data 100 is shown, the
compensation for the joint spacing is performed both in distal and
posterior approaches. Thus, the joint compensation points relative to the
femur reference data are determined. As will be discussed later in this
Detailed Description, the joint compensation points relative to the femur
reference data will be used to determine the joint compensation relative
to the femur implant.

[0209]As can be understood from FIG. 16, which is a y-z plane wherein the
joint compensation points are shown, the posterior plane S and the distal
plane P are moved away in the direction of normal of plane S and P
respectively by the adjustment value tr. In one embodiment, the
adjustment value tr is equal to the cartilage thickness. That is, the
joint compensation points will be determined relative to the posterior
plane S and the distal plane P which are moved away in the direction of
normal of plane S and P, respectively, by an amount equal to the
cartilage thickness. In some embodiments, the adjustment value tr is
equal to one-half of the joint spacing. That is, the joint compensation
points will be determined relative to the posterior plane S and the
distal plane P which are moved away in the direction of normal of plane S
and P, respectively, by an amount equal one-half the joint spacing. In
other words, the femoral implant accounts for half of the joint spacing
compensation, while the tibia implant will account for the other half of
the joint spacing compensation.

[0210]As can be understood from FIG. 15, the femur reference data 100 was
uploaded onto a coordinate system, as described above. To compensate for
the joint spacing, the distal line-D1D2 is moved closer to the
distal plane-P by an amount equal to the adjustment value tr, thereby
resulting in joint spacing compensation points D1J, D2J and
line D1JD2J. The distal plane P was previously moved by
adjustment value tr. Similarly, posterior reference line P1P2 is moved
closer to the posterior plane-S by an amount equal to the adjustment
value tr, thereby resulting in joint spacing compensation points
P1J, P2J and line P1JP2J. The trochlear groove
reference line-line GO does not move and remains as the reference line
for the joint spacing compensation. Lines D1JD2J and
P1JP2J will be stored and utilized later for an analysis
related to the femoral implant silhouette curve.

[0211]4. Selecting the Sizes for the Femoral Implants

[0212]The next steps are designed to select an appropriate implant size
such that the implant will be positioned within the available degrees of
freedom and may be optimized by 2D optimization. There are 6 degrees of
freedom for a femoral implant to be moved and rotated for placement on
the femur. For example, the translation in the x direction is fixed based
on the reference planes-S and P and sagittal slices of femur as shown in
FIGS. 4 and 7C. Rotation around the y axis, which corresponds to the
varus/valgus adjustment is fixed based on the reference lines determined
by analysis of the coronal slices, namely, lines EF and AB, and coronal
plane-S as shown in FIGS. 4 and 7B. Rotation around the z axis, which
corresponds to internal/external rotation, is fixed by the trochlear
groove reference line, line GO or TGB, axial-distal reference line, line
CD, and axial-posterior reference line, line AB, as shown in the axial
views in FIGS. 4 and 6A-6E. By fixing these three degrees of freedom, the
position of the implant can be determined so that the outer silhouette
line of the implant passes through both the distal reference line and
posterior reference line. Optimization will search for a sub-optimal
placement of the implant such that an additional angle of flange contact
is greater than but relatively close to 7 degrees. Thus, by constraining
the 3 degrees of freedom, the appropriate implant can be determined.

[0213]a. Overview of Selection of Femoral Implant

[0214]Based on previously determined femoral implant data 100', as shown
in FIGS. 11-13, a set of 3 possible sizes of implants are chosen. For
each implant, the outer 2D silhouette curve of the articular surface of
the candidate implant model is computed and projected onto a y-z plane,
as shown in FIGS. 20A-20C. The calculated points of the silhouette curve
are stored. Then, the sagittal slice corresponding to the inflection
point 500 (see FIG. 21A) is found and the corresponding segmentation
spline is considered and the information is stored. Then an iterative
closest point alignment is devised to find the transform to match the
implant to the femur.

[0215]The next sections of this Detailed Description will now discuss the
process for determining the appropriate implant candidate, with reference
to FIGS. 17-22.

[0216]i. Implant Selection

[0217]In one embodiment, there is a limited number of sizes of a candidate
femoral implant. For example, one manufacturer may supply six sizes of
femoral implants and another manufacturer may supply eight or another
number of femoral implants. A first implant candidate 700 (see FIG. 17)
may be chosen based on the distance L' between the posterior and distal
reference lines P1'P2' and D1'D2' determined above in
FIG. 13, with reference to the femoral implant reference data 100'. The
distance L' of the candidate implants may be stored in a database and can
be retrieved from the implant catalogue. In some embodiments, a second
and third implant candidate 702, 704 (not shown) may be chosen based on
the distance L between the posterior and distal reference lines
P1P2 and D1D2 of the femur 28' determined above in
FIG. 8, with reference to the femoral reference data 100 and distance L'.
First implant candidate 700 has the same distance L as the patient femur.
Second implant candidate 702 is one size smaller than the first implant
candidate 700. Third implant candidate 704 is one size larger than the
first implant candidate 700. In some embodiments, more than 3 implant
candidates may be chosen.

[0218]The following steps 2-6 are performed for each of the implant
candidates 700, 702, 704 in order to select the appropriate femoral
implant 34'.

[0219]ii. Gross Alignment of Implant onto Femur

[0220]In some embodiments, the gross alignment of the implant 34' onto the
femur 28' may be by comparison of the implant reference data 100' and the
femur reference data 100. In some embodiments, gross alignment may be via
comparison of the medial-lateral extents of both the implant and the
femur. In some embodiments, both gross alignment techniques may be used.

[0221]In some embodiments, as shown in FIG. 17, which shows the implant
34' placed onto the same coordinate plane with the femur reference data
100, the implant candidate may be aligned with the femur. Alignment with
the femur may be based on the previously determined implant reference
lines D1'D2' and P1'P2' and femur reference lines
D1D2 and P1P2.

[0222]In some embodiments, and as can be understood from FIGS. 18A-18C and
19A-19C, the medial lateral extent of the femur and the implant can be
determined and compared to ensure the proper initial alignment. FIG. 18A
is a plan view of the joint side 240 of the femur implant model 34'
depicted in FIG. 3B. FIG. 18B is an axial end view of the femur lower end
200 of the femur bone model 28' depicted in FIG. 3A. The views depicted
in FIGS. 18A and 18B are used to select the proper size for the femoral
implant model 34'.

[0223]As can be understood from FIG. 18A, each femoral implant available
via the various implant manufacturers may be represented by a specific
femoral implant 3D computer model 34' having a size and dimensions
specific to the actual femoral implant. Thus, the representative implant
model 34' of FIG. 18A may have an associated size and associated
dimensions in the form of, for example, an anterior-posterior extent iAP
and medial-lateral extent iML, which data can be computed and stored in a
database. These implant extents iAP, iML may be compared to the
dimensions of the femur slices from the patient's actual femur 18. For
example, the femur bone 18 may have dimensions such as, for example, an
anterior-proximal extent bAP and a medial-lateral extent bML, as shown in
FIG. 18B. In FIG. 18A, the anterior-posterior extent iAP of the femoral
implant model 34' is measured from the anterior edge 270 to the posterior
edge 275 of the femoral implant model 34', and the medial-lateral extent
iML is measured from the medial edge 280 to the lateral edge 285 of the
femoral implant model 34'.

[0224]Each patient has femurs that are unique in size and configuration
from the femurs of other patients. Accordingly, each femur slice will be
unique in size and configuration to match the size and configuration of
the femur medically imaged. As can be understood from FIG. 18B, the
femoral anterior-posterior length bAP is measured from the anterior edge
290 of the patellofemoral groove to the posterior edge 295 of the femoral
condyle, and the femoral medial-lateral length bML is measured from the
medial edge 300 of the medial condyle to the lateral edge 305 of the
lateral condyle. The implant extents iAP and iML and the femur extents
bAP, bML may be aligned for proper implant placement as shown in FIG. 18C
and along the direction of axial-distal reference line-CD.

[0225]As can be understood from FIGS. 19A-19C, these medial-lateral
extents of the implant iML and femur bML can be measured from the 2D
slices of the femur of FIG. 5A. For example, FIG. 19A, which shows the
most medial edge of the femur in a 2D sagittal slice and FIG. 19B, which
shows the most lateral edge of the femur in a 2D sagittal slice, can be
used to calculate the bML of the femur 28'. The implant 34' will be
centered between the medial and lateral edges, as shown in FIG. 19C,
which is a 2D slice in coronal view showing the medial and lateral edges,
thereby grossly aligning the implant with the femur.

[0226]iii. Determine Outer Silhouette Curve of Implant in y-z Plane

[0227]The silhouette of the femoral implant is the curve formed by
farthest points from center in y-z plane projection of the femoral
implant geometry. The points of the silhouette curve may be utilized to
confirm placement of the implant onto the femur based on the femur
reference lines that have been altered to account for the joint
compensation.

[0228]For a discussion of the process for determining the points of the
silhouette curve of the femoral implant, reference is now made to FIGS.
20A-20C. As can be understood from FIG. 20A, which is an implant 34'
mapped onto a y-z plane, the points of a candidate implant are retrieved
from the implant database. The points are then imported onto a y-z plane
and the silhouette curve can be determined. The silhouette curve 34''' is
determined by finding the points that are the farthest from the center
along an outer circumference 35 of the articular surface of the implant
34'. FIG. 20B, which is the silhouette curve 34''' of the implant 34',
shows the result of the silhouette curve calculations. The silhouette
curve data is then imported into a y-z plane that includes the joint
spacing compensation data, as shown in FIG. 20C, which is the silhouette
curve 34''' aligned with the joint spacing compensation points
D1JD2J and P1JP2J. The resulting joint spacing
compensation and silhouette curve data 800 (e.g. D1'''D2'''
P1'''P2''') is stored for later analysis.

[0230]The flange point is determined and stored. As can be understood from
FIG. 21A, which shows a distal femur 28' with an implant 34', the distal
femur is analyzed and the flange point 500 of the implant 34' is
determined relative to the anterior surface 502 of the distal end of a
femur condyle 28'. FIG. 21B, which depicts a femur implant 34',
illustrates the location of the flange point 500 on the implant 34' as
determined by an analysis such as one illustrated in FIG. 21A.

[0231]The anterior cut plane 504 is determined and stored. The range of
the anterior cut plane of the implant is determined such that the cut
plane (and therefore the implant) is within certain tolerances. As shown
in FIG. 21A, a cut plane 504 is determined based on the location of the
implant 34' on the femur 28'. An angle A between the cut plane 504 and
the flange point 500 is between approximately 7 and approximately 15
degrees. In some embodiments, the angle A is approximately 7 degrees. In
some embodiments, the distal cut plane may be found as described below
with respect to the final verification step. For each respective implant,
the anterior cut plane and the distal cut plane are at a fixed angle for
the implant. That is, once the anterior cut plane is found, the distal
cut plane can be determined relative to the fixed angle and the anterior
cut plane. Alternatively, once the distal cut plane is found, the
anterior cut plane can be determined relative to the fixed angle and the
distal cut plane.

[0232]The inflection point 506 is determined and stored. As shown in FIG.
21C, which shows a slice of the distal femur 28' in the sagittal view,
the inflection point 506 is located on the anterior shaft of the spline
508 of femur 28' where the flange point 500 of the implant 34' is in
contact with the femur 28'. An implant matching algorithm will match the
flange point 500 of implant 34' to the spline 508 of the femur at
approximately the inflection point 506 of the femur 28'. As can be
understood from FIG. 21D, which shows the implant 34' positioned on the
femur 28', the implant 34' should be aligned to touch the distal and
posterior reference planes P, S respectively to reach proper alignment.
In one embodiment, the implant matching algorithm is a customized
extension of an algorithm known as iterative closest point matching.

[0233]The next section of the Detailed Description now discusses how the
data and data points determined above and stored for future analysis will
be used in the selection of an appropriate implant.

[0234]v. Determine Points of Set A and Set B

[0235]Determination of the data sets contained in Set A and Set B aid in
determining the appropriate implant and ensuring that the chosen implant
mates with the femur within certain tolerances.

[0236]The joint spacing compensation points D1JD2J and
P1JP2J were determined as described with reference to FIG. 16
and are added to Set A. Next, the joint spacing compensation points
D1JD2J and P1JP2J are matched to the closest
respective points on the silhouette curve, as shown in FIG. 20C, thereby
resulting in points D1'''D2''' and P1'''P2''' or the
joint spacing compensation and silhouette curve data 800. Points
D1'''D2''' and P1'''P2''' will be added to Set B.

[0237]The inflection point and flange point data are analyzed. An
inflection point 506' is found to represent the inflection point 506 that
is closest in proximity to the flange point 500, which were both
discussed with reference to FIGS. 21A-21D. The point 506' is added to Set
A. The flange point 500 is then projected to a y-z plane. The resulting
flange point 500' is added to Set B.

[0238]Thus, Set A contains the following points: the joint spacing
compensation points D1JD2J and P1JP2J and the
inflection point 506'. Set B contains the following points: Points
D1'''D2''' and P1'''P2''' (the joint spacing
compensation and silhouette curve data 800) and the flange point 500'.

[0239]vi. Utilize the Data of Sets A and B

[0240]Find a rigid body transform. The data points of Set A and Set B are
compared and a rigid body transform that most closely matches Set A to
Set B is chosen. The rigid body transform will transform an object
without scaling or deforming. That is, the rigid body transform will show
a change of position and orientation of the object. The chosen transform
will have rotation about the x-axis and translation in the y-z plane.

[0241]Find the inverse of the rigid body transform. The inverse of this
rigid body transform is then imported into the y-z plane that also
contains the femur reference lines D1D2 and P1P2 and
the femur spline 508 that corresponds to the flange point 500 of the
implant 34'.

[0242]The steps described in subsections iv, v and vi of subsection D4(a)
of this Detailed Description are repeated until the relative motion is
within a small tolerance. In one embodiment, the steps are repeated fifty
times. In some embodiments, the steps are repeated more than fifty times
or less than fifty times.

[0243]In some embodiments, and as shown in FIG. 22A, an acceptable
translation in y-z plane may be determined. FIG. 22A depicts an implant
that is improperly aligned on a femur, but shows the range of the search
for an acceptable angle A. Within this range for angle A, the translation
in y-z leads to finding the rigid body transform as described above. In
some embodiments, the process may optimize y-z translation and rotation
around the x-axis in one step. This can be done by rotating the implant
silhouette curve by several half degree increments and then, for each
increment, performing the steps described in subsections iv, v and vi of
subsection D4(a) of this Detailed Description. Translation in the y-z
axis only occurs during the analysis utilizing the inverse of the rigid
body transform.

[0245]By using the above outlined procedure, an appropriate implant is
found by choosing the implant and transform combination that provides an
inflection angle that is greater than 7 degrees but closest to 7 degrees,
as explained with reference to FIG. 21A.

[0246]In some embodiments, an additional verification step is performed by
placing the implant 34' in the MRI with the transform 28''' that is found
by the above described method. As can be understood from FIG. 22B, which
illustrates the implant positioned on the femur transform wherein a femur
cut plane is shown, during the verification step, a user may determine
the amount of bone that is cut J1 on the medial and lateral condyles
by looking at the distal cut plane 514 of the implant 34'. J1 is
determined such that the thickness of the bone cut on both the medial and
lateral sides is such that the bone is flat after the cut. Multiple
slices in both the distal and medial areas of the bone can be viewed to
verify J1 is of proper thickness.

[0247]Once an appropriate femur implant is chosen, the preoperative
planning process turns to the selection of an appropriate tibia implant.
The tibia planning process includes a determination of the tibia
reference lines to help determine the proper placement of the tibia
implant. The candidate tibia implant is placed relative to the tibia
reference lines and placement is confirmed based on comparison with
several 2D segmentation splines.

[0248]E. Tibia Planning Process

[0249]For a discussion of the tibia planning process, reference is now
made to FIGS. 23-32D. FIGS. 23-26B illustrate a process in the POP
wherein the system 10 utilizes 2D imaging slices (e.g., MRI slices, CT
slices, etc.) to determine tibia reference data, such as reference points
and reference lines, relative to the undamaged side of the tibia plateau.
The resulting tibia reference data 900 is then mapped or projected to an
x-y plane (axial plane). A candidate tibia implant is chosen, which
selection will be discussed with reference to FIGS. 27A-C. The tibia
implant placement is adjusted and confirmed relative to the tibia, as
discussed in more detail below with reference to FIGS. 28-32D.

[0250]1. Determining Tibia Reference Data

[0251]For a discussion of a process used to determine the tibia reference
data 900, reference is now made to FIGS. 23-27B. As can be understood
from FIG. 23, which is a top view of the tibia plateaus 404, 406 of a
tibia bone image or model 28'', the tibia reference data 900 may include
reference points (e.g. Q1, Q1'), reference lines (e.g.
T1T2, V1) and a reference plane (e.g. S') (see FIGS.
26A-26B). In some embodiments, the tibia reference data 900 may also
include the anterior-posterior extant (tAP) and the medial-lateral extant
(tML) of the tibia 28'' (see FIGS. 27A-27B). As shown in FIG. 23, each
tibia plateau 404, 406 includes a curved recessed condyle contacting
surface 421, 422 that is generally concave extending anterior/posterior
and medial/lateral. Each curved recessed surface 421, 422 is generally
oval in shape and includes an anterior curved edge 423, 424 and a
posterior curved edge 425, 426 that respectively generally define the
anterior and posterior boundaries of the condyle contacting surfaces 421,
422 of the tibia plateaus 404, 406. Depending on the patient, the medial
tibia plateau 406 may have curved edges 424, 426 that are slightly more
defined than the curved edges 423, 425 of the lateral tibia plateau 404.

[0252]a. Identify Points Q1, Q2 and Q1', Q2'

[0253]2D slices in the sagittal view are analyzed to determine the tibia
flexion/extension adjustment. Anterior tangent lines TQ1, TQ2
can be extended tangentially to the most anterior location on each
anterior curved edge 423, 424 to identify the most anterior points
Q1, Q2 of the anterior curved edges 423, 424. Posterior tangent
lines TQ1', TQ2' can be extended tangentially to the most
posterior location on each posterior curved edge 425, 426 to identify the
most posterior points Q1', Q2' of the posterior curved edges 425, 426.
Thus, in one embodiment, the lateral side tibia plateau 404 can be
analyzed via tangent lines to identify the highest points Q1, Q1'. For
example, tangent line TQ1 can be used to identify the anterior
highest point Q1, and tangent line TQ1' can be used to identify the
posterior highest point Q1'. In some embodiments, a vector V1 extending
between the highest points Q1, Q1' may be generally perpendicular to the
tangent lines TQ1, TQ1'. Similarly, the medial side tibia
plateau 406 can be analyzed via tangent lines to identify the highest
points Q2, Q2'. For example, tangent line TQ2 can be used to
identify the anterior highest point Q2, and tangent line TQ2' can be
used to identify the posterior highest point Q2'. In some embodiments, a
vector V2 extending between the highest points Q2, Q2' may be generally
perpendicular to the tangent lines TQ2, TQ2'.

[0254]i. Confirm points Q1, Q2 and Q1', Q2'

[0255]As can be understood from FIGS. 24A-24D, the location of Q1, Q1', Q2
and Q2' may also be confirmed by an analysis of the appropriate sagittal
slice. As shown in FIG. 24A, which is a sagittal cross section through a
lateral tibia plateau 404 of the tibia model or image 28', points Q1 and
Q1' can be identified as the most anterior and posterior points,
respectively, of the curved recessed condyle contacting surface 421 of
the lateral tibia plateau 404. As shown in FIG. 24B, which is a sagittal
cross section through a medial tibia plateau 406 of the tibia model 28'',
points Q2 and Q2' can be identified as the most anterior and posterior
points, respectively, of the curved recessed condyle contacting surface
422 of the medial tibia plateau 406. Such anterior and posterior points
may correspond to the highest points of the anterior and posterior
portions of the respective tibia plateaus.

[0256]b. Determine lines V1 and V2

[0257]As can be understood from FIGS. 23-24B, line V1 extends through
anterior and posterior points Q1, Q1', and line V2 extends through
anterior and posterior points Q2, Q2'. Line V1 is a lateral
anterior-posterior reference line. Line V2 is a medial posterior-anterior
reference line. Each line V1, V2 may align with the lowest point of the
anterior-posterior extending groove/valley that is the elliptical
recessed tibia plateau surface 421, 422. The lowest point of the
anterior-posterior extending groove/valley of the elliptical recessed
tibia plateau surface 421, 422 may be determined via ellipsoid calculus.
Each line V1, V2 will be generally parallel to the anterior-posterior
extending valleys of its respective elliptical recessed tibia plateau
surface 421, 422 and will be generally perpendicular to its respective
tangent lines TQ1, TQ1', TQ2, TQ2'. The
anterior-posterior extending valleys of the elliptical recessed tibia
plateau surfaces 421, 422 and the lines V1, V2 aligned therewith may be
generally parallel. The planes associated with lines V1 and V2 are
generally parallel or nearly parallel to the joint line of the knee
joint, as determined above.

[0258]Depending on the patient, the medial tibia plateau 406 may be
undamaged or less damaged than the lateral tibia plateau 404. In such a
case, the reference points Q2, Q2' and reference line V2 of the medial
plateau 406 may be used to establish one or more reference points and the
reference line of the damaged lateral tibia plateau. FIG. 24C depicts a
sagittal cross section through an undamaged or little damaged medial
tibia plateau 406 of the tibia model 28'', wherein osteophytes 432 are
also shown. As indicated in FIG. 24C, the points Q2, Q2' can be located
on the undamaged medial plateau and set as reference points. The
anterior-posterior reference line, line V2, can be constructed by
connecting the anterior and posterior reference points Q2, Q2'. The
reference line V2 from the undamaged or little damaged medial side is
saved for use in determining the reference line of the lateral tibia
plateau in the case where the lateral tibia plateau is damaged. For
example, as shown in FIG. 24D, which is a sagittal cross section through
a damaged lateral tibia plateau 404 of the tibia model 28'', the anterior
point Q1 is found to be undamaged. In this case, the established
reference line V2 from the medial plateau can be applied to the damaged
lateral plateau by aligning the reference line V2 with point Q1. By doing
so, the reference line V1 of the lateral plateau can be established such
that line V1 touches the reference point Q1 and extends through the
damaged area 403. Thus, the reference line V1 in the lateral plateau is
aligned to be parallel or nearly parallel to the reference line V2 in the
medial plateau. While the above described process is described in terms
of extrapolating one or more reference lines of a damaged lateral plateau
from an analysis of the undamaged medial tibia plateau, it is understood
that the same process can be undertaken where the lateral tibia plateau
is undamaged and one or more reference lines of a damaged medial plateau
can be extrapolated from the lateral tibia plateau.

[0259]In other embodiments, as can be understood from FIG. 24D and
assuming the damage to the lateral tibia plateau 404 is not so extensive
that at least one of the highest anterior or posterior points Q1, Q1'
still exists, the damaged tibia plateau 404 can be analyzed via tangent
lines to identify the surviving high point Q1, Q1'. For example, if the
damage to the lateral tibia plateau 404 was concentrated in the posterior
region such that the posterior highest point Q1' no longer existed, the
tangent line TQ1 could be used to identify the anterior highest
point Q1. Similarly, if the damage to the medial tibia plateau 406 was
concentrated in the anterior region such that the anterior highest point
Q1' no longer existed, the tangent line TQ1' could be used to
identify the posterior highest point Q1'. In some embodiments, a vector
extending between the highest points Q1, Q1' may be generally
perpendicular to the tangent lines TQ1, TQ1'.

[0260]c. Determine Reference Points T1 and T2 and Reference Line T1T2

[0261]2D slices in both the axial and coronal views are analyzed to
determine the varus/valgus adjustment by finding the reference points T1
and T2. As shown in FIGS. 25A-25B, which are coronal and axial 2D slices
of the tibia, reference points T1 and T2 are determined by an analysis of
the most proximal coronal slice (FIG. 25A) and the most proximal axial
slice (FIG. 25B). As indicated in FIG. 25A, in which the tibia is shown
in a 0° knee extension, reference points T1 and T2 are determined.
The points T1 and T2 represent the lowest extremity of tangent contact
points on each of the lateral and medial tibia plateaus, respectively. In
one embodiment, tangent points T1 and T2 are located within the region
between the tibia spine and the medial and lateral epicondyle edges of
the tibia plateau, where the slopes of tangent lines in this region are
steady and constant. For example, and as shown in FIG. 25A, the tangent
point T1 is in the lateral plateau in Area I between the lateral side of
the lateral intercondylar tubercle to the attachment of the lateral
collateral ligament. For the medial portion, the tangent point T2 is in
Area II between the medial side of the medial intercondylar tubercle to
the medial condyle of the tibia.

[0262]As shown in FIG. 25B, the most proximal slice of the tibia in the
axial view is analyzed to find reference points T1 and T2. As above,
reference points T1 and T2 represent the lowest extremity of tangent
contact points on each of the lateral and medial tibia plateaus. Once the
reference points T1 and T2 are found in both the coronal and axial views,
a line T1T2 is found.

[0263]A line T1T2 is created by extending a line between reference points
T1 and T2. In some embodiments, the coronal and axial slices are viewed
simultaneously in order to align the lateral and medial
anterior-posterior reference lines V1 and V2. As shown in FIG. 23, the
lateral and medial anterior-posterior reference lines V1 and V2 are
generally perpendicular or nearly perpendicular to line T1T2.

[0264]d. Determine the Approximate ACL Attachment Point (AE) and the
Approximate PCL Attachment Point (PE) of the Tibia and Reference Line
AEPE

[0265]As can be understood from FIGS. 23 and 25B, the reference points
representing the approximate anterior cruciate ligament (ACL) attachment
point of the tibia AE and the approximate posterior cruciate ligament
(PCL) attachment point of the tibia PE are determined. The reference
point AE can be determined by finding the approximate tibia attachment
point for the ACL. The reference point PE can be determined by finding
the approximate tibia attachment point for the PCL. The line AEPE
connects through reference points AE and PE and may also be referred to
as an ACL/PCL bisector line.

[0266]e. Confirm Location of Tibia Reference Data

[0267]As can be understood from FIG. 23, the tibia reference data 900
includes reference points and reference lines that help to define
flexion/extension adjustment, varus/valgus adjustment and
internal/external rotation. For example, the tibia flexion/extension
adjustment is determined by an analysis of the sagittal images as shown
in FIGS. 24A-D, which determine reference points Q1, Q1', Q2, Q2'. The
tibia varus/valgus adjustment may be found by an analysis of FIG. 25A and
finding reference points T1, T2 and reference line T1T2. As can be
understood from FIG. 23, the proximal reference line, line T1T2, defines
the internal/external rotation as shown in an axial view (line T1T2 in
FIG. 25B) and the varus/valgus angle as shown in a coronal view (line
T1T2 in FIG. 25A).

[0268]The location of the reference points and reference lines may also be
confirmed based on their spatial relationship to each other. For example,
as shown in FIGS. 23-24B, the anterior-posterior reference lines V1, V2
of the tibia plateau are generally parallel to the ACL/PCL bisector
reference line, line AEPE. As indicated in FIGS. 23 and 25B, the
axial-proximal reference line, line T1T2 is perpendicular or nearly
perpendicular to anterior-posterior reference lines V1, V2. As shown in
FIG. 23, the tangent lines TQ1, TQ2, TQ1', TQ2' are
perpendicular or nearly perpendicular to the ACL/PCL bisector reference
line, line AEPE.

[0269]f. Mapping the Tibia Reference Data to an x-y Plane

[0270]As can be understood from FIGS. 26A-26B, which depict the tibia
reference data 900 on a coordinate system (FIG. 26A) and on a proximal
end of the tibia (FIG. 26B), the tibia reference data 900 is mapped to an
x-y coordinate system to aid in the selection of an appropriate tibia
implant. As shown in FIG. 26A, the endpoints Q1, Q1', Q2, Q2' and their
respective anterior posterior reference lines V1 and V2 and the endpoints
T1, T2 and the proximal reference line T1T2 are each mapped to the
reference plane. In addition, and as shown in FIG. 26B, the reference
data 900 may be imported onto a 3D model of the tibia 28'' for
verification purposes. The tibia reference data 900 is stored for later
analysis.

[0271]2. Selecting Tibia Implant Candidate

[0272]There are six degrees of freedom for placing the tibial implant onto
the tibia. The reference points and reference lines determined above will
constrain all but 2 degrees of freedom which are translated in the x-y
plane. The sizing and positioning of the tibia implant (and the femoral
component) will be verified with a 2D view of the knee and components.

[0273]As briefly discussed above with reference to FIGS. 1A and 1C, when
selecting the tibia implant model 34'' corresponding to the appropriate
tibia implant size to be used in the actual arthroplasty procedure, the
system 4 may use one of at least two approaches to select the appropriate
size for a tibia implant [block 115]. In one embodiment, the tibia
implant is chosen based on the size of the femoral implant that was
determined above. In some embodiments, as discussed with reference to
FIGS. 27A-27C, the system 4 determines the tibial anterior-posterior
length tAP and the tibial medial-lateral length tML and the tibia implant
34'' can be selected based on the anterior-posterior extent tAP of the
proximal tibia. In some embodiments, the tibia implant may be selected
based on both the tibial anterior-posterior length tAP and the tibial
medial-lateral length tML

[0274]In one embodiment, there is a limited number of sizes of a candidate
tibia implant. For example, one manufacturer may supply six sizes of
tibia implants and another manufacturer may supply eight or another
number of tibia implants. The anterior-posterior length jAP and
medial-lateral length jML dimensions of these candidate implants may be
stored in a database. The tAP and tML are compared to the jAP and jML of
candidate tibia implants stored in the database.

[0275]FIG. 27A is a 2D sagittal image slice of the tibia wherein a
segmentation spline with an AP extant is shown. FIG. 27B is an axial end
view of the tibia upper end of the tibia bone image or model 28''
depicted in FIG. 3A. FIG. 27C is a plan view of the joint side 255 of the
tibia implant model 34'' depicted in FIG. 3B. The views depicted in FIGS.
27A-27C are used to select the proper size for the tibial implant model
34''. The tibia implant may be chosen based on the maximum tAP extent as
measured in an analysis of the segmentation spine as shown in FIG. 27A.

[0276]Each patient has tibias that are unique in size and configuration
from the tibias of other patients. Accordingly, each tibia bone model
28'' will be unique in size and configuration to match the size and
configuration of the tibia medically imaged. As can be understood from
FIG. 27B, the tibial anterior-posterior length tAP is measured from the
anterior edge 335 of the tibial bone model 28'' to the posterior edge 330
of the tibial bone model 28'', and the tibial medial-lateral length tML
is measured from the medial edge 340 of the medial plateau of the tibia
bone model 28'' to the lateral edge 345 of the lateral plateau of the
tibia bone model 28''.

[0277]As can be understood from FIG. 27C, each tibial implant available
via the various implant manufacturers may be represented by a specific
tibia implant 3D computer model 34'' having a size and dimensions
specific to the actual tibia implant. Thus, the representative implant
model 34'' of FIG. 3D may have an associated size and associated
dimensions in the form of, for example, anterior-proximal extent tAP and
the medial-lateral extent tML of the tibia model 34'', as shown in FIG.
27B. In FIG. 27C, the anterior-posterior extent jAP of the tibia implant
model 34'' is measured from the anterior edge 315 to the posterior edge
310 of the tibial implant model 34'', and the medial-lateral extent jML
is measured from the medial edge 320 to the lateral edge 325 of the
tibial implant model 34''. Once the tibia implant candidate 34'' is
chosen, the reference lines jML, jAP of the implant candidate 34'' are
stored by the system 4 for later analysis.

[0278]3. Determine Tibia Implant Reference Data

[0279]As can be understood from FIG. 28, which is a top view of the tibia
plateaus 404', 406' of a tibia implant model 34'', wherein the tibia
implant reference data 900' is shown, the tibia reference data 900' may
include tangent points q1, q1', q2, q2' and corresponding
anterior-posterior reference lines V3, V4 and intersection points t1, t2
and its corresponding proximal reference line t1t2.

[0280]In order to define the implant reference data 900' relative to the
tibia model 28'', the implant reference lines jML, jAP are imported into
the same x-y plane with the tibia reference data 900 that was previously
mapped to the x-y plane. For gross alignment purposes, the medial-lateral
extent jML of the tibia implant 34'' is aligned with the proximal
reference line T1T2 of the tibia model 28''. Then, the tibia reference
data 900' is determined. The implant 34'' and the bone model 28'' may
then undergo additional alignment processes.

[0281]a. Determine Tangent Points q1, q1', q2, q2'

[0282]As shown in FIG. 28, each tibia plateau 404', 406' includes a curved
recessed condyle contacting surface 421', 422' that is generally concave
extending anterior/posterior and medial/lateral. Each curved recessed
surface 421', 422' is generally oval in shape and includes an anterior
curved edge 423', 424' and a posterior curved edge 425', 426' that
respectively generally define the anterior and posterior boundaries of
the condyle contacting surfaces 421', 422' of the tibia plateaus 404',
406'. Thus, the lateral tangent points q1, q1' can be identified as the
most anterior and posterior points, respectively, of the curved recessed
condyle contacting surface 421' of the lateral tibia plateau 404'. The
medial tangent points q2, q2' can be identified as the most anterior and
posterior points, respectively, of the curved recessed condyle contacting
surface 422' of the medial tibia plateau 406'.

[0283]b. Determine Reference Lines V3 and V4

[0284]As can be understood from FIG. 28, line V3 extends through anterior
and posterior points q1, q1', and line V4 extends through anterior and
posterior points q2, q2'. Line V3 is a lateral anterior-posterior
reference line. Line V4 is a medial posterior-anterior reference line.
Each line V3, V4 may align with the lowest point of the
anterior-posterior extending groove/valley that is the elliptical
recessed tibia plateau surface 421', 422'. The lowest point of the
anterior-posterior extending groove/valley of the elliptical recessed
tibia plateau surface 421', 422' may be determined via ellipsoid
calculus. Each line V3, V4 will be generally parallel to the
anterior-posterior extending valleys of its respective elliptical
recessed tibia plateau surface 421', 422'. The length of the reference
lines V3, V4 can be determined and stored for later analysis.

[0286]As shown in FIG. 28, the intersection or reference points t1, t2
represent the midpoints of the respective surfaces of the lateral tibia
plateau 404' and the medial tibia plateau 406'. Also, each intersection
point t1, t2 may represent the most distally recessed point in the
respective tibia plateau 404', 406'. An implant proximal reference line
t1t2 is created by extending a line between the lateral and medial lowest
reference points t1, t2. The length of the reference line t1t2 can be
determined and stored for later analysis. This line t1t2 is parallel or
generally parallel to the joint line of the knee. Also, as indicated in
FIG. 28, the tibia implant 34'' includes a base member 780 for being
secured to the proximal tibia 28''.

[0288]As can be understood from FIGS. 28 and 26A, the implant reference
data 900' specifies the position and orientation of the tibia implant
34'' and generally aligns with similar data 900 from the tibia bone model
28''. Thus, the lateral tangent points q1, q1' and medial tangent points
q2, q2' of the implant 34'' generally align with the lateral tangent
points Q1, Q1' and medial tangent points Q2, Q2' of the tibia 28''. The
anterior posterior reference lines V3, V4 of the implant 34'' generally
align with the anterior posterior reference lines V1, V2 of the tibia
model 28''. The intersection points t1, t2 of the implant 34'' generally
align with the reference points T1, T2 of the tibia 28''. The proximal
reference line t1t2 of the implant 34'' generally aligns with the
proximal reference line T1T2 of the tibia 28''. Reference line t1t2 is
approximately perpendicular to the anterior-posterior reference lines V3,
V4.

[0289]The implant reference data 900' lies on a coordinate frame, plane
r'. The tibia reference data 900 lies on a coordinate frame, plane s'.
Thus, the alignment of the implant 34'' with the tibia 28'' is the
transformation between the two coordinate frames plane r', plane s'.
Thus, the gross alignment includes aligning the proximal line t1t2 of the
implant 34'' to the proximal line T1T2 of the tibia 28''. Then, in a
further alignment process, the reference points t1, t2 of the implant and
the reference points T1, T2 of the tibia 28'' are aligned. The implant
34'' is rotated such that the sagittal lines of the implant 34'' (e.g.
V3, V4) are parallel or generally parallel to the sagittal lines of the
tibia 28'' (e.g. V1, V2). Once the tibia 28'' and the implant 34'' are in
alignment (via the reference data 900, 900'), the tibial cut plane can be
determined.

[0290]4. Determine Surgical Cut Plane for Tibia

[0291]a. Determine Cut Plane of the Tibia Implant

[0292]The cut plane of the tibia implant is determined. The user may
determine this cut plane by a method such as one described with respect
to FIGS. 29A-29C. FIG. 29A is an isometric view of the 3D tibia bone
model 1002 showing the surgical cut plane SCP design. FIGS. 29B and 29C
are sagittal MRI views of the surgical tibia cut plane SCP design with
the posterior cruciate ligament PCL.

[0293]During the TKA surgery, the damaged bone surface portions of the
proximal tibia will be resected from the cut plane level 850 and be
removed by the surgeon. As shown in FIGS. 29B and 29C, the surgical
tibial cut plane 850 may be positioned above the surface where the PCL is
attached, thereby providing for the maintenance of the PCL during TKA
surgery.

[0294]FIG. 30A is an isometric view of the tibia implant 34'' wherein a
cut plane r1 is shown. As can be understood from FIG. 30A, the cut plane
r1 of the implant 34'' is the surgical tibial cut plane 850 and is a data
point or set of data points that may be stored in the implant database.
In order to determine whether an adjustment to the cut plane r1 must be
made, the cut plane r1 of the tibia implant 34'' is aligned with the
tibia 28''.

[0295]b. Determine Initial Cut Plane of the Tibia

[0296]As shown in FIG. 30B, which is a top axial view of the implant 34''
superimposed on the tibia reference data 900, the implant 34'' is opened
with the tibia reference data 900 and is generally aligned with the tibia
reference data 900 at the level of the cut plane r1 by the system 4.
However, the implant 34'' is not centered relative to the tibia reference
data 900. The anterior/posterior extent tAP'' and medial/lateral extent
tML'' of the tibia 28'' at the cut level are found.

[0297]The implant 34'' may be centered by the system (or manually by a
user of the system). As indicated in FIG. 30C, which is an axial view of
the tibial implant aligned with the tibia reference data 900, the tibia
implant 34'' is then centered relative to the anterior posterior extent
tAP'' and the medial lateral extents tML'' of the tibia 28''.

[0298]c. Determine Joint Line and Adjustment

[0299]In order to allow an actual physical arthroplasty implant to restore
the patient's knee to the knee's pre-degenerated or natural configuration
with the its natural alignment and natural tensioning in the ligaments,
the condylar surfaces of the actual physical implant generally replicate
the condylar surfaces of the pre-degenerated joint bone. In one
embodiment of the systems and methods disclosed herein, condylar surfaces
of the bone model 28'' are surface matched to the condylar surfaces of
the implant model 34''. However, because the bone model 28'' may be bone
only and not reflect the presence of the cartilage that actually extends
over the pre-degenerated condylar surfaces, the surface matching of the
modeled condylar surfaces may be adjusted to account for cartilage or
proper spacing between the condylar surfaces of the cooperating actual
physical implants (e.g., an actual physical femoral implant and an actual
physical tibia implant) used to restore the joint such that the actual
physical condylar surfaces of the actual physical cooperating implants
will generally contact and interact in a manner substantially similar to
the way the cartilage covered condylar surfaces of the pre-degenerated
femur and tibia contacted and interacted.

[0300]i. Determine Adjustment Value tr

[0301]Thus, in one embodiment, the implant model is modified or
positionally adjusted (via e.g. the tibia cut plane) to achieve the
proper spacing between the femur and tibia implants. To achieve the
correct adjustment or joint spacing compensation, an adjustment value tr
may be determined. In one embodiment, the adjustment value tr that is
used to adjust the implant location may be based off of an analysis
associated with cartilage thickness. In another embodiment, the
adjustment value tr used to adjust the implant location may be based off
of an analysis of proper joint gap spacing, as described above with
respect to FIGS. 14G and 14H. Both of the methods are discussed below in
turn.

[0302]1. Determining Cartilage Thickness

[0303]FIG. 30D is a MRI image slice of the medial portion of the proximal
tibia and indicates the establishment of landmarks for the tibia POP
design. FIG. 30E is a MRI image slice of the lateral portion of the
proximal tibia. The wm in FIG. 30D represents the cartilage thickness of
the medial tibia meniscus, and the wl in FIG. 30E represents the
cartilage thickness of the lateral tibia meniscus. In one embodiment, the
cartilage thicknesses wl and wm are measured for the tibia meniscus for
both the lateral and medial plateaus 760, 765 via the MRI slices depicted
in FIGS. 30D and 30E. The measured thicknesses may be compared. If the
cartilage loss is observed for the medial plateau 765, then the
wlmin of lateral plateau 760 is selected as the minimum cartilage
thickness. Similarly, if the lateral plateau 760 is damaged due to
cartilage loss, then the wmmin of medial plateau 765 is selected as
the minimum cartilage thickness. The minimum cartilage wr may be
illustrated in the formula, wr=min (wm, wl). In one embodiment, for
purposes of the adjustment to the tibia, the adjustment value tr may be
may be equal to the minimum cartilage value wr.

[0304]2. Determining Joint Gap

[0305]In one embodiment, the joint gap is analyzed as discussed above with
respect to FIGS. 14G and 14H to determine the restored joint line gap
Gp3. In one embodiment, for purposes of the adjustment to the tibia shape
matching, the adjustment value tr may be calculated as being half of the
value for Gp3, or in other words, tr=Gp3/2.

[0306]d. Determine Compensation for Joint Spacing

[0307]After centering the implant 34'' within the cut plane, joint spacing
compensation is taken into account. As shown in FIG. 30F, which is an
isometric view of the tibia implant and the cut plane, the implant 34''
and cut plane-r1 are moved in a direction that is generally perpendicular
to both the proximal and sagittal reference lines by an amount equal to
adjustment value tr, thereby creating an adjusted cut plane r1'. In one
embodiment, the adjustment value tr is equal to approximately one-half of
the joint spacing. In other embodiments, the adjustment value tr is equal
to the cartilage thickness.

[0308]Thus, the implant candidate may be selected relative to the joint
spacing compensation that was determined previously with reference to
FIGS. 14G, 14H, 30D and 30E. As discussed above, in one embodiment, once
the joint spacing compensation is determined, one-half of the joint
spacing compensation will be factored in to the femur planning process
and one-half of the joint spacing compensation will be factored in to the
tibia planning process. That is, the femur implant is adjusted by an
amount equal to one-half of the joint spacing compensation. Thus, the
candidate femur implant will be chosen such that when it is positioned on
the femur relative to the joint spacing compensation, the candidate
implant will approximate the pre-degenerated joint line. Similarly, the
tibia implant is adjusted by an amount equal to one-half of the joint
spacing compensation. Thus, the candidate tibia implant will be chosen
such that when it is positioned on the tibia relative to the joint
spacing compensation, the candidate implant will approximate the
pre-degenerated joint line. Also, the tibia implant mounting post 780
(see FIG. 31B) and the femur implant mounting post 781 (see FIG. 31A)
will be oriented at approximately the center of the tibia and femur.

[0309]F. Verification of Implant Planning Models and Generation of
Surgical Jigs Based on Planning Model Information

[0310]FIGS. 31A1-32 illustrate one embodiment of a verification process
that may be utilized for the preoperative planning process disclosed
herein. FIGS. 31A1-31B are sagittal views of a 2D image slice of the
femur 28' (FIGS. 31A1 and 31A2) and the tibia 28'' (FIG. 31B) wherein the
2D computer generated implant models 34 are also shown. As can be
understood from FIGS. 31A1-31B, verification for both the distal femur
and proximal tibia is performed by checking the reference lines/planes in
2D sagittal views. The reference lines/planes may also be checked in
other views (e.g. coronal or axial). For example, and as can be
understood from FIGS. 31A1 and 31A2, for the femur planning model, the
flexion-extension rotation is verified by checking whether the inflection
point 506 of the anterior cortex of the femur 28' sufficiently contacts
the interior surface 510 of the anterior flange 512 of implant 34'. That
is, as can be understood from FIG. 31A2, when the implant 34' is properly
aligned with the femur 28', the flange point 500 of the implant should
touch the inflection point of the segmentation spline or femur 28'.

[0311]As can be understood with reference to FIG. 31B, the tibia planning
may be verified by looking at a 2D sagittal slice. Depending on the
initial planning choice made above, one of the following can be verified:
1) whether the size of the tibial implant 34'' matches or corresponds
with the size of the femoral implant 34', or 2) whether the tibial
implant 34'' is one size larger or one size smaller than the femoral
implant 34' size (e.g., a size 2 femur, and a size 1 tibia; or a size 2
femur, and a size 2 tibia; or a size 2 femur, and a size 3 tibia). In
other embodiments, the size of tibial implant may be chosen without
taking into account the size of the femoral implant. One of skill in the
art will recognize that different implant manufacturers may utilize a
different naming convention to describe different sizes of implants. The
examples provided herein are provided for illustrative purposes and are
not intended to be limiting.

[0312]As indicated in FIG. 31B, the placement of the tibial implant can be
verified by viewing the anterior and posterior positions of the implant
34'' relative to the tibial bone 28''. If the implant is properly
positioned, the implant should not extend beyond the posterior or
anterior edge of the tibia bone. The flexion-extension of the tibia 28''
can be verified by checking that the tibial implant reference line 906,
which is a line segment approximating the normal direction of the
implant's proximal surface, is at least parallel with the posterior
surface 904 of the tibia 28'' or converging with the posterior tibial
surface 906 around the distal terminus of the tibial shaft.

[0313]In other embodiments, as shown in FIGS. 32A-32G and FIGS. 33A-33C,
the planning can also be confirmed from generated 3D bone models 1000,
1002 and 3D implant models 1004, 1006. If the planning is done
incorrectly, the reference lines 100, 100', 900, 900' will be corrected
in the 2D MRI views to amend the planning. FIGS. 32A-32C and FIGS.
32E-32G are various views of the implant 3D models 1004, 1006
superimposed on the 3D bone models 1000, 1002. FIG. 32D is a coronal view
of the bone models 1000, 1002.

[0314]FIGS. 32A-32G show an embodiment of the POP system disclosed herein.
The alignment of the implant models 1004, 1006 with the bone models 1000,
1002 is checked in the anterior view (FIG. 32A), the posterior view (FIG.
32E), the lateral view (FIG. 32B), the medial view (FIG. 32C), the top
view (FIG. 32F) and the bottom view (FIG. 32G).

[0315]The flexion/extension between the femur and tibia implant models
1004, 1006 and the femur and tibia bone models 1000, 1002 is examined in
both the medial view and the lateral view. For example, FIG. 32B shows
the lateral view wherein the knee is shown in full extension or 0 degree
flexion and in its natural alignment similar to its pre-arthritis status
(e.g., neutral, varus or valgus), and FIG. 32C shows the medial view of
the knee in full extension or 0 degree flexion and in its natural
alignment (e.g., neutral, varus or valgus).

[0316]FIG. 32D shows the varus/valgus alignment of the knee model 28m',
28m'' with the absence of the implants 34m', 34m''. The gaps Gp4, Gp5
between the lowermost portions of distal femoral condyles 302, 303 and
the lowermost portions of the tibia plateau 404, 406 will be measured in
the femoral and tibia bone models 28m', 28m''. Gap Gp4 represents the
distance between the distal lateral femoral condyle 302 and the lateral
tibial plateau 404. Gap Gp5 represents the distance between the distal
medial femoral condyle 303 and the medial tibial plateau 406. In the
varus/valgus rotation and alignment, Gp4 is substantially equal to Gp5,
or |Gp4-Gp5|<<1 mm. FIG. 32D shows the knee model 28m', 28m'' that
is intended to restore the patient's knee back to his pre-OA stage.

[0317]The IR/ER rotation between the femur and tibia implant models 1004,
1006 and the femur and tibia bone models 1000, 1002 is examined in both
the top and bottom views. For example, FIG. 32F shows the top view of the
tibia showing the IR/ER rotation between no flexion and high flexion, and
FIG. 32G shows the bottom view of the femur showing the IR/ER rotation
between no flexion and high flexion. The stem of the tibia implant model
1006 and the surgical cut plane of the tibia implant model 1006 provide
the information for the IR/ER rotation.

[0318]FIGS. 33A-33C show another embodiment of the POP system disclosed
herein. FIG. 33A is an medial view of the 3D bone models. FIG. 33B is an
medial view of the 3D implant models. FIG. 33C is an medial view of the
3D implant models superimposed on the 3D bone models.

[0319]As shown in FIG. 33A, a 3D model of the femur bone 1000 and a 3D
model of the tibia bone 1002 may be generated from the 2D segmentation
splines of image slices and the reference data 100, 900 determined above
for verification of the POP. As shown in FIG. 33B, a 3D model of the
femur implant 1004 and a 3D model of the tibia implant 1006 may be
generated based on the reference lines 100', 900' determined above for
verification of the POP. The implant models 1004, 1006 and the bone
models 1000, 1002 are aligned based on the reference lines in a 3D
computer modeling environment and the alignment is checked in the
sagittal view as shown in FIG. 33C. If the alignment of the bone models
1000, 1002 and the implant models 1004, 1006 is not correct, the
reference lines 100, 100', 900, 900' will be corrected in the 2D views to
amend the planning.

[0320]The knee model 28', 28'', 1000, 1002 and associated implant models
34', 34'', 1004, 1006 developed through the above-discussed processes
include dimensions, features and orientations that the system 10 depicted
in FIG. 1A can be utilized to generate 3D models of femur and tibia
cutting jigs 2. The 3D model information regarding the cutting jigs can
then be provided to a CNC machine 10 to machine the jigs 2 from a polymer
or other material.

[0321]G. Mechanical Axis Alignment

[0322]While much of the preceding disclosure is provided in the context of
achieving natural alignment for the patient's knee post implantation of
the actual physical femur and tibia implants, it should be noted that the
systems and methods disclosed herein can be readily modified to produce
an arthroplasty jig 2 that would achieve a zero degree mechanical axis
alignment for the patient's knee post implantation.

[0323]For example, in one embodiment, the surgeon utilizes a natural
alignment femoral arthroplasty jig 2A as depicted in FIGS. 2A and 2B to
complete the first distal resection in the patient's femoral condylar
region. Instead of utilizing a natural alignment tibia arthroplasty jig
2B as depicted in FIGS. 2C and 2D, the surgeon instead completes the
first proximal resection in the patient's tibia plateau region via free
hand or a mechanical axis guide to cause the patient's tibia implant to
result in a mechanical axis alignment or an alignment based off of the
mechanical axis (e.g., an alignment that is approximately one to
approximately three degrees varus or valgus relative to zero degree
mechanical axis).

[0324]In one embodiment, as indicated in FIGS. 34A-35B, the arthroplasty
jigs 2AM and 2BM may be configured to provide bone resections that lead
to natural alignment, mechanical axis alignment or alignments in between
the two. For example, the jigs 2AM and 2BM may have a natural alignment
saw slot 123 and one or more non-natural alignment saw slots 123', 123''
and 123''' that may, for example, be one degree, two degrees, three
degrees or some other incremental measurement away from natural alignment
and towards zero degree mechanical axis alignment. The surgeon may select
a two degree deviation slot 123'' based on a physical inspection and
surgical experience.

[0325]In one embodiment of the POP systems and methods disclosed herein,
instead of superposing the 3D bone models 1000, 1002 to the 3D implant
models 1004, 1006 in a manner that results in the saw cut and drill hole
data 44 that leads to the production of natural alignment arthroplasty
jigs 2A, 2B, the superposing of the bone and implant models 1000, 1002,
1004, 1006 may be conducted such that the resulting saw cut and drill
hole data 44 leads to the production of zero degree mechanical axis
alignment arthroplasty jigs or some other type of arthroplasty jig
deviating in a desired manner from zero degree mechanical axis.

[0326]Thus, depending on the type of arthroplasty jig desired, the systems
and methods disclosed herein may be applied to both the production of
natural alignment arthroplasty jigs, zero degree mechanical axis
alignment jigs, or arthroplasty jigs configured to provide a result that
is somewhere between natural alignment and zero degree mechanical axis
alignment.

[0327]Although the present invention has been described with reference to
preferred embodiments, persons skilled in the art will recognize that
changes may be made in form and detail without departing from the spirit
and scope of the invention.